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Description

Name: N/A

Alias: Grimmi

Gender: Female

Age: 24
Birthday: 1st November

Occupation: Vigilante / Bin loader

Appearance:
Grimmi stands at 5'10.5", with messy brown hair and eyes. The skin of her hands, neck and ears are black due to the effect of her quirk, and she has piercings in her ears. She has long lower lashes and fangs. Her usual outfit considers of baggy trousers, black knee length boots with white reinforcements at the feet, a tattered dark green coat, a loose white shirt and black and white gloves that help protect the world around her of her quirk.
She has dark eyebags from a bad sleep schedule, mostly due to her job and general bad life choices.

Personality:
Grimmi is a generally pleasant individual who minds her own business.
While not anti-social, Grimmi makes a point to act as a bit of a loner, not wanting to get attached to people who could potentially hurt her. Due to her trust issues because of her past, Grimmi is paranoid that those around her are out to get or use her. She very much has a "me against the world" mentally.
She feels emotions very passionately and genuinely, making no effort to hide how she feels, which makes her quite uncomfortable to be around if she gets angry or upset. Which does not happen often, but when it does, Grimmi can become nasty or even violent as a way to protect herself from her source of her fury.
Due to her trust issues, Grimmi is very picky about the people she likes or talks to, which causes her to miss out on opportunities to make friends and healthy connections.
She'd much rather enjoy company from a distance, enjoying people watching and generally just vibing.

Despite her trust issues, Grimmi has a huge respect for authority, specifically the individuals she has witnessed doing actual good and efforts in the world. She deeply respects those who can stand alone against the world and make something of themselves through hard work and dedication. On the other hand, she despises leeches and those that ride on the coattails of the more successful, which is where her distrust of sidekicks comes from.
While she deeply respects heroes, especially the top 10 heroes, she's suspicious of their sidekicks, which is why she targets and tests them in her vigilante work.
If someone can't prove themselves to her (whether they realize it or not), they will never be able to get on Grimmi's good side. While she won't hurt them, she'll never trust them and always be hostile. Meanwhile, with those she decides she likes and trusts, she's much more lenient and forgiving, even if they end up hurting her in some way, she'll still like them and hope that they'll see their errors and change for the better.

Likes: Heroes (her favourite is Burnin'), hero merchandise (she collects it), iced coffee, early morning lights, ambitious/motivated/hardworking people

Dislikes: People who are leeches, traffic, pouring rain, people knowing her true identity/origin, her quirk

Notable relationships
Her parents
While they mutually love each other, Grimmi has a huge distrust of her father based on his unfaithful behavior towards her mother. She also judges her mother for not standing up against her husband and generally being quite meek, despite respecting her for being a hard worker. Both were loving and provided Grimmi with everything she needed, supporting through her childhood struggles of being excluded by the other children.
However, as she grew older, she realised her father was a cheater in more ways than one, constantly made false promises of change or would straight up deny his flaws and reject criticism. Changing stories, rewriting history, denying and deflecting, never taking responsibility. So while she still loves him, she feels constant distress at the mere thought of him.
She misses them both, especially her mother, but with the addition of her past actions, she can't bring herself to seek them out and reunite with them.
Jaggers
After she ran away from home, Jaggers was hired by her parents to find her. While he did find her, she begged him to not tell her parents.
So, he lied and provided her a home in Musutafu, far away from her original hometown.
While not directly in charge of her, Jaggers and Grimmi do have a relaxed mentor/student relationship, and they care for each other, Jaggers being one of the few people Grimmi fully trusts. He keeps an eye out for her, makes sure she's taking care of herself, but doesn't dictate what she should do with her life and doesn't intervene with her vigilante actions.
He has helped her with training and enhancing her skills.
Weirdo and his kids
She knows nothing about Weirdo other than him and Jaggers are old friends and that Weirdo is some sort of mercenary. She doesn't question it.
However, she adores his kids, Francis, Melinda and Barnabas (Baz) and often babysits and looks after them. She's aggressively protective of them and will annihilate anybody who hurts them. She likes to take them out for fast food and other unhealthy treats, and basically acts a big sister to them.
Endeavor
When she was five years old, Endeavor saved her and her father from an villain attack. Ever since then, despite his generally hostile and unwelcoming image, Grimmi has been in absolute awe of him, and respects his hard work and career. Even when his past actions came to light due to Dabi's video, Grimmi couldn't help but respect his response to it, seeing him taking responsibility, bearing the burden of hero society and making an actual move to change.
Grimmi sees Endeavor as a man her father will never be, a terrible father who is taking full responsibility without question or expectations from others.
She can't help but respect him for it, and wishes her father would do the same.
Overhaul / Shie Hassaikai
Due to the nature of her quirk and vigilante actions, she has been sought out by the Overhaul and his associates.
They have a mutual dislike, Chisaki seeing her as 'dirty' because of her quirk, and Grimmi not liking his whole evil shtick.
Both having hand based destructive quirks, they've made a deal to stay out of each other's business and nobody gets hurt.
Grimmi knows nothing of their actions or intent, just knows that if she ever tried to bring vigilante justice onto them, they would for sure kill her and Jaggers (she's more concerned about the latter than herself).
She can't help but feel a smidge of awe for Chisaki and his ambitious attitude, but she hates that she does and would like to kick his butt.
League of Villains (and villains in general)
Absolutely hates them and everything they're about, especially Dabi (mainly because he stinks).
She hates Mr Compress and Spinner the least, and can appreciate all of their hard work/ambitiousness, but hates the way they go about things, especially any "vengeance" aspect of their actions, as she believes vengeful feelings to be pathetic and a waste of time.
While they have tried to recruit her for their cause due to her vigilante status and quirk, she's made it clear that she's no tool to be used for a greater purpose she honestly doesn't care about. This has made her a bit of a liability that they'd like to get rid of now, but seeing how she's only a minor threat not interested in being involved and they're busy with their plans, she's mostly been left alone, if a little tormented by Dabi.

Abilities:
-Competent at hand-to-hand combat; she's very aggressive and attacks to wound, going for all the softs spots, especially the eyes. Very much a dirty fighter, not caring for honour and prioritizing self-preservation.
-Great sense of direction; being a bin loader, she knows the layout of locations well and generally knows exactly where she is, good hiding spots and the such.
-Leg power; her legs are her strongest body parts, being able to use the most strength and force there. You don't want to get kicked.
-Keen problem solving; Grimmi is quirk and efficient at coming up with the best solution for any problem, whether it is a villain attack or being stuck out in the rain. She's very observant and notices lots of little details around her than can be of use for solving problems or getting out of difficult situations.
-Tenacious and stubborn; despite her self-preservation, Grimmi knows her limits and how to push them without breaking herself further than needed, so she's a pain to deal with because she will do anything to achiever her current goal/purpose while controlling the damage done to her.
-Enhanced reflexes; especially when it comes to dodging/escaping, Grimmi is very receptive to attacks and getting from them, being annoyingly hard to hit.

Quirk: Engulf
A lethal hand-based quirk, anything she touches when activated is engulfed in darkness, turning black before dissipating into nothingness. While she has amazing control of it now, if she starts to panic or freak out, she can start losing control and engulf things and people she doesn't mean to. It's essentially impossible to stop the engulfing unless you cut off part of the body that is affected, but the process is almost instantaneous, so you have to be fast.
Darkness:
This ultimate move of Grimmi engulfs a select location in complete darkness, essentially creating a prison of darkness that can only be broken when Grimmi is weakened, either by tiring her out or beating her up. The more compact the area, the more powerful Darkness is. Grimmi has to be physically present in the location for the ability to last. When in effect, the victim is unable to see anything in the sea of darkness and must depend on their other senses to find Grimmi.
From the outside, the location is completely engulfed in black, and if somebody tries to touch it, they get dragged into the Darkness and trapped. Grimmi can push people out if she wants, which makes it a great ability to give time for others to escape.
If a victim stays any longer than five minutes in the Darkness, they start being engulfed themselves. At the moment, Grimmi can only keep this ability going for ten minutes, and it completely knocks her out afterwards, unable to muster any strength.
Weakness:
If she overuses her ability, by activating Darkness for too long or trying to engulf something too big (like a building or giant), her quirk will start engulfing her from the inside, forming black cracks all over her body, starting from her neck and arms. If she stops and gives herself time to heal, she'll be fine, but if she pushes too far, she'll end up engulfed and killed by her own quirk, so she has to be careful.

Backstory:
Brought up as a single child under a different name, Grimmi has always been rather alone, especially after her quirk manifested when she was two.
The nature of her quirk scared the other children and a lot of adults, but her parents were there to support her, so while she felt lonely, she wasn't too affected. But she still grew a disdain for her quirk.
When she was five, her father and her were saved from a villain attack by Endeavor, sparking her love and respect for heroes. She never wanted to be a hero, too worried about her villain-like quirk to consider it. But she did want to help heroes in some way, either by become a policewoman or some other type of helpful job.

As she started growing up, she felt more and more lonely without any friends, so she started becoming a people pleaser, doing whatever she could to gain friends. Doing others' homework, doing presentations alone, taking all the burden of group projects, essentially being used in every way just for the chance of making a friend. However, despite this and her generally friendly attitude, the other kids were too freaked out by her quirk to really want to hang out with her, which caused her to feel deep frustration and anger at the world. Instead of dealing with it however, she just pushed it down, thinking that it'll eventually get better and that she could ignore the bad feelings.

By the end of middle school, she came to the realization that her dad was unfaithful to her mother, often being seen with other women, causing scandals and general drama. On top of that, he kept changing jobs, always thinking he was too good for his position, having a certain sense of entitled, thinking he was owed the world but wouldn't work for it. While he was good and took care of Grimmi, she always felt it was hypocritical of him and she confronted him often. For years, he made continuous promises to change, to be better, to get help, but he never did, always relapsing into his bad habits. It came to a point where he deflected the accusations and became defensive when Grimmi pointed out his hypocrisy.
She also started becoming frustrated with her mother for not standing up to her husband and his behavior. She was simply too busy trying to support the family, as she was the main breadwinner because her father couldn't keep a proper job. So whenever Grimmi pointed out her father's action, her mother would just sigh sadly and say nothing.
While they provided her with everything she needed, she started feeling like she was living a lie. They pretended to be a "good family" while they were splitting apart, only getting worse the more entitled her father became. It eventually turned into emotional neglect, where not even Grimmi would care for her own feelings, just choking them down and playing pretend. She believed it was easier to keep the peace than confront her father and cause an argument yet again. Just like her mother.

This all came crashing down in her first year of high school.
A group of delinquents found out about her quirk and starting including her in their group. Happy to finally have friends, Grimmi completely missed all the red flags, not realizing their true intentions. They hung out for weeks before they eventually invited her to their 'outings', which turned out to be a series of petty crimes. They wanted her to use her quirk to destroy any evidence of their actions, and for a little while, desperate to be accepted, she did. But as the petty crimes became more and more serious, from sneaking candy bars from convenience stores to full on home invasions, Grimmi started feeling a huge sense of guilt that even her parents noticed her change in behaviour.
Terrified of their potential disappointment in her, Grimmi told her "friends" she didn't want to use her quirk for them anymore. The delinquents didn't like that, saying she knew too much and that tattling would only get her in trouble as well. Grimmi didn't want to tattle, she just wanted to stop, not break the law anymore. However, the group didn't believe her and they started threatening her with violence and ruining her reputation in school even more than it already was.
Terrified of this change in attitude, Grimmi started running away, only to be chased down by the group. She was eventually cornered by their leader, a boy named Kei, who started getting aggressive with her. In fear and panic, all her stifled emotions of frustration, anger and distress exploded and she activated her quirk in self-defense, which engulfed and dissipated Kei, killing him.

When she realised what she had done, Grimmi freaked out. She ran away, refusing to go home and admit her actions, horrified and humiliated with what she had done. When she didn't return home that night, her parents claimed her as missing, getting the police to search for her. However she hid out behind some outside bins, using the darkness to hide her from the authorities, thinking they were coming to arrest her for what she had done. Too scared to stay in her hometown, she left it altogether, with nothing but the clothes she was wearing.
When more than a day went by and she was nowhere to be found, the police and her parents called Jaggers, a private detective with a quirk that could track others down using their blood, to find her. Using some of her blood found in the location where she had been attacked by Kei (unknown to the police), Jaggers confirmed it was hers and tracked the blood with the police following him.

He eventually found Grimmi in the next town over, hungry, dirty and wet from the rain, but refusing to go home. She begged him not to tell her parents, explaining to situation when he pushed her to. There was something different about Jaggers, and she knew he wouldn't be angry at her actions, so she admitted everything, including her family problems.
He listened. He reminded her that she was only 16, just about to end her first year of high school. She should go home, she wouldn't be in trouble, it was in self-defense. Grimmi cried, saying everybody was scared of her already before she had even done anything, there was no way she'd be accepted or even tolerated now. Jaggers insisted she go home, seeing how he had a job to do.
Grimmi refused, saying she'd just runaway again, she couldn't be with her parents anymore. She couldn't pretend anymore, what little control she had had shattered the second she killed Kei, she wouldn't be able to act as if nothing happened and her family would have to confront their problems or bury their heads further in the ground.
Grimmi couldn't cope with either.

Seeing how distressed and shattered Grimmi was, and knowing what hero society was like, Jaggers caved. He claimed to the police that the trail had gone cold, washed away by the rain, so he had no way of finding Grimmi now. Once the police had returned to her hometown, Jaggers collected Grimmi and brought her to Musutafu where he set her up with a small apartment and job there, working as a bin loader. Nobody asked questions, anybody who associates with Jaggers never asks questions. Grimmi appreciated that.

For the next two years, Jaggers helped her form a new identity, now officially going by Grimmi. He helped her finish her high school studies by homeschooling, so that she at least had that. He also helped her train and control her quirk, so she'd be able to protect herself without killing anyone, as that seemed to distress her. She also met Weirdo and his kids that appeared out of nowhere through the years. She has no real relation with Weirdo, but loves his kids and often babysits them.

As she turned eighteen, her love and admiration for heroes only grew. However, she started becoming skeptical of sidekicks and some of the lower ranking heroes.
Due to her past of being used and leeched off of, she saw anybody that used the stronger heroes as a stepping stool into the hero industry as morally corrupt and weak.
She started 'testing' new sidekicks and heroes. This is where her vigilante work starts.

Whenever a new hero or sidekick was announced, she'd research everything about them. Depending on her research, she'd either approve of him, excited to see their potential, or be highly skeptical of them, and desire to test them.
She searches for the newbies when they're out alone in hero attire, and use her move Darkness on them. Depending on how they react to the attack and how quickly they cave in to her taunts (generally demeaning them and acting all villain-y), Grimmi would decide if she likes them or not.
If they figure out her weakness and are able to get a punch against her, or at least always stand strong, never showing weakness or giving in, Grimmi could find it in herself to respect that about them, and let them go.
However, if they start flailing, cowering or generally not being heroic, giving into her taunts or showing similar weakness, she loses any potential respect and only further torments them, only stopping once the engulfing process starts. She never kills them, but makes sure they know she doesn't approve of them. That if they crumble so quickly when against her, they'll never be able to stand strong against actual threats.
By that point, a lot of those she tests retire almost immediately. Some of them do continue as heroes, but she makes sure to bad mouth them wherever she goes, calling them lazy, corrupt, pathetic or whatever else.

She's most intense about sidekicks for the top 10 heroes, as she sees top heroes as the best, and so any sidekicks they get should also be the best. Especially when it comes to Endeavor's. Seeing how he saved her when she was little, she holds him to a higher standard and refuses to believe he'd ever accept anybody below amazing into his agency. This mean that for the past six years, whenever he'd get a new sidekick, they'd all report some quirk that trapped them in darkness for five minutes while being taunted by a voice who eventually 'approved of them' and let them go.
Endeavor has been trying to capture this vigilante, but seeing how Grimmi isn't stupid enough to confront Endeavor directly, she's always sneaky and random about her attacks.

When she was twenty, after a couple years of her vigilante work and being something of a lesser known urban legend, she was approached by the Shie Hassaikai. Overhaul wanted to see what she was about, and was less than impressed. The feelings were mutual, Grimmi immediately disliking him and his attitude to her. Knowing they'd be able to mutually destroy each other, they decided to make a deal. If she stayed out of their business, they'd stay out hers, as a sort of hostile co-existence. Not wanting to bring Jaggers any problems, Grimmi agreed, knowing that the police had they eyes on them anyway.
She stopped seeing Weirdo and his kids around this time, as they moved away for the safety of the children.

Around the time when the Nomus started popping up, Grimmi was approached by the League of Villains to join them, but she flat out refused, as she hates villains. They argued over morality for a while, Shigaraki and Grimmi getting on each other's nerves endlessly, eventually coming to a similar deal as with Overhaul; if they leave her alone, she leaves them alone. Despite that, they occasionally lurked around her just to keep an eye on her actions and making sure she didn't do anything that would hinder them. Whenever Dabi was the one coming to check on her, Grimmi was ready to throw hands, even though she knew she had no chance of beating him. Once things started getting serious with their plans and the heroes, they stopped checking on her, and now Grimmi is bunking with Jaggers while the war is happening, too worried about her quirk accidentally killing someone to get involved. She only helps whenever Jaggers is out looking for trapped or lost civilians, who they then help get to safe zones.

Description

Name: N/A

Alias: Grimmi

Gender: Female

Age: 24
Birthday: 1st November

Occupation: Vigilante / Bin loader

Appearance:
Grimmi stands at 5'10.5", with messy brown hair and eyes. The skin of her hands, neck and ears are black due to the effect of her quirk, and she has piercings in her ears. She has long lower lashes and fangs. Her usual outfit considers of baggy trousers, black knee length boots with white reinforcements at the feet, a tattered dark green coat, a loose white shirt and black and white gloves that help protect the world around her of her quirk.
She has dark eyebags from a bad sleep schedule, mostly due to her job and general bad life choices.

Personality:
Grimmi is a generally pleasant individual who minds her own business.
While not anti-social, Grimmi makes a point to act as a bit of a loner, not wanting to get attached to people who could potentially hurt her. Due to her trust issues because of her past, Grimmi is paranoid that those around her are out to get or use her. She very much has a "me against the world" mentally.
She feels emotions very passionately and genuinely, making no effort to hide how she feels, which makes her quite uncomfortable to be around if she gets angry or upset. Which does not happen often, but when it does, Grimmi can become nasty or even violent as a way to protect herself from her source of her fury.
Due to her trust issues, Grimmi is very picky about the people she likes or talks to, which causes her to miss out on opportunities to make friends and healthy connections.
She'd much rather enjoy company from a distance, enjoying people watching and generally just vibing.

Despite her trust issues, Grimmi has a huge respect for authority, specifically the individuals she has witnessed doing actual good and efforts in the world. She deeply respects those who can stand alone against the world and make something of themselves through hard work and dedication. On the other hand, she despises leeches and those that ride on the coattails of the more successful, which is where her distrust of sidekicks comes from.
While she deeply respects heroes, especially the top 10 heroes, she's suspicious of their sidekicks, which is why she targets and tests them in her vigilante work.
If someone can't prove themselves to her (whether they realize it or not), they will never be able to get on Grimmi's good side. While she won't hurt them, she'll never trust them and always be hostile. Meanwhile, with those she decides she likes and trusts, she's much more lenient and forgiving, even if they end up hurting her in some way, she'll still like them and hope that they'll see their errors and change for the better.

Likes: Heroes (her favourite is Burnin'), hero merchandise (she collects it), iced coffee, early morning lights, ambitious/motivated/hardworking people

Dislikes: People who are leeches, traffic, pouring rain, people knowing her true identity/origin, her quirk

Notable relationships
Her parents
While they mutually love each other, Grimmi has a huge distrust of her father based on his unfaithful behavior towards her mother. She also judges her mother for not standing up against her husband and generally being quite meek, despite respecting her for being a hard worker. Both were loving and provided Grimmi with everything she needed, supporting through her childhood struggles of being excluded by the other children.
However, as she grew older, she realised her father was a cheater in more ways than one, constantly made false promises of change or would straight up deny his flaws and reject criticism. Changing stories, rewriting history, denying and deflecting, never taking responsibility. So while she still loves him, she feels constant distress at the mere thought of him.
She misses them both, especially her mother, but with the addition of her past actions, she can't bring herself to seek them out and reunite with them.
Jaggers
After she ran away from home, Jaggers was hired by her parents to find her. While he did find her, she begged him to not tell her parents.
So, he lied and provided her a home in Musutafu, far away from her original hometown.
While not directly in charge of her, Jaggers and Grimmi do have a relaxed mentor/student relationship, and they care for each other, Jaggers being one of the few people Grimmi fully trusts. He keeps an eye out for her, makes sure she's taking care of herself, but doesn't dictate what she should do with her life and doesn't intervene with her vigilante actions.
He has helped her with training and enhancing her skills.
Weirdo and his kids
She knows nothing about Weirdo other than him and Jaggers are old friends and that Weirdo is some sort of mercenary. She doesn't question it.
However, she adores his kids, Francis, Melinda and Barnabas (Baz) and often babysits and looks after them. She's aggressively protective of them and will annihilate anybody who hurts them. She likes to take them out for fast food and other unhealthy treats, and basically acts a big sister to them.
Endeavor
When she was five years old, Endeavor saved her and her father from an villain attack. Ever since then, despite his generally hostile and unwelcoming image, Grimmi has been in absolute awe of him, and respects his hard work and career. Even when his past actions came to light due to Dabi's video, Grimmi couldn't help but respect his response to it, seeing him taking responsibility, bearing the burden of hero society and making an actual move to change.
Grimmi sees Endeavor as a man her father will never be, a terrible father who is taking full responsibility without question or expectations from others.
She can't help but respect him for it, and wishes her father would do the same.
Overhaul / Shie Hassaikai
Due to the nature of her quirk and vigilante actions, she has been sought out by the Overhaul and his associates.
They have a mutual dislike, Chisaki seeing her as 'dirty' because of her quirk, and Grimmi not liking his whole evil shtick.
Both having hand based destructive quirks, they've made a deal to stay out of each other's business and nobody gets hurt.
Grimmi knows nothing of their actions or intent, just knows that if she ever tried to bring vigilante justice onto them, they would for sure kill her and Jaggers (she's more concerned about the latter than herself).
She can't help but feel a smidge of awe for Chisaki and his ambitious attitude, but she hates that she does and would like to kick his butt.
League of Villains (and villains in general)
Absolutely hates them and everything they're about, especially Dabi (mainly because he stinks).
She hates Mr Compress and Spinner the least, and can appreciate all of their hard work/ambitiousness, but hates the way they go about things, especially any "vengeance" aspect of their actions, as she believes vengeful feelings to be pathetic and a waste of time.
While they have tried to recruit her for their cause due to her vigilante status and quirk, she's made it clear that she's no tool to be used for a greater purpose she honestly doesn't care about. This has made her a bit of a liability that they'd like to get rid of now, but seeing how she's only a minor threat not interested in being involved and they're busy with their plans, she's mostly been left alone, if a little tormented by Dabi.

Abilities:
-Competent at hand-to-hand combat; she's very aggressive and attacks to wound, going for all the softs spots, especially the eyes. Very much a dirty fighter, not caring for honour and prioritizing self-preservation.
-Great sense of direction; being a bin loader, she knows the layout of locations well and generally knows exactly where she is, good hiding spots and the such.
-Leg power; her legs are her strongest body parts, being able to use the most strength and force there. You don't want to get kicked.
-Keen problem solving; Grimmi is quirk and efficient at coming up with the best solution for any problem, whether it is a villain attack or being stuck out in the rain. She's very observant and notices lots of little details around her than can be of use for solving problems or getting out of difficult situations.
-Tenacious and stubborn; despite her self-preservation, Grimmi knows her limits and how to push them without breaking herself further than needed, so she's a pain to deal with because she will do anything to achiever her current goal/purpose while controlling the damage done to her.
-Enhanced reflexes; especially when it comes to dodging/escaping, Grimmi is very receptive to attacks and getting from them, being annoyingly hard to hit.

Quirk: Engulf
A lethal hand-based quirk, anything she touches when activated is engulfed in darkness, turning black before dissipating into nothingness. While she has amazing control of it now, if she starts to panic or freak out, she can start losing control and engulf things and people she doesn't mean to. It's essentially impossible to stop the engulfing unless you cut off part of the body that is affected, but the process is almost instantaneous, so you have to be fast.
Darkness:
This ultimate move of Grimmi engulfs a select location in complete darkness, essentially creating a prison of darkness that can only be broken when Grimmi is weakened, either by tiring her out or beating her up. The more compact the area, the more powerful Darkness is. Grimmi has to be physically present in the location for the ability to last. When in effect, the victim is unable to see anything in the sea of darkness and must depend on their other senses to find Grimmi.
From the outside, the location is completely engulfed in black, and if somebody tries to touch it, they get dragged into the Darkness and trapped. Grimmi can push people out if she wants, which makes it a great ability to give time for others to escape.
If a victim stays any longer than five minutes in the Darkness, they start being engulfed themselves. At the moment, Grimmi can only keep this ability going for ten minutes, and it completely knocks her out afterwards, unable to muster any strength.
Weakness:
If she overuses her ability, by activating Darkness for too long or trying to engulf something too big (like a building or giant), her quirk will start engulfing her from the inside, forming black cracks all over her body, starting from her neck and arms. If she stops and gives herself time to heal, she'll be fine, but if she pushes too far, she'll end up engulfed and killed by her own quirk, so she has to be careful.

Backstory:
Brought up as a single child under a different name, Grimmi has always been rather alone, especially after her quirk manifested when she was two.
The nature of her quirk scared the other children and a lot of adults, but her parents were there to support her, so while she felt lonely, she wasn't too affected. But she still grew a disdain for her quirk.
When she was five, her father and her were saved from a villain attack by Endeavor, sparking her love and respect for heroes. She never wanted to be a hero, too worried about her villain-like quirk to consider it. But she did want to help heroes in some way, either by become a policewoman or some other type of helpful job.

As she started growing up, she felt more and more lonely without any friends, so she started becoming a people pleaser, doing whatever she could to gain friends. Doing others' homework, doing presentations alone, taking all the burden of group projects, essentially being used in every way just for the chance of making a friend. However, despite this and her generally friendly attitude, the other kids were too freaked out by her quirk to really want to hang out with her, which caused her to feel deep frustration and anger at the world. Instead of dealing with it however, she just pushed it down, thinking that it'll eventually get better and that she could ignore the bad feelings.

By the end of middle school, she came to the realization that her dad was unfaithful to her mother, often being seen with other women, causing scandals and general drama. On top of that, he kept changing jobs, always thinking he was too good for his position, having a certain sense of entitled, thinking he was owed the world but wouldn't work for it. While he was good and took care of Grimmi, she always felt it was hypocritical of him and she confronted him often. For years, he made continuous promises to change, to be better, to get help, but he never did, always relapsing into his bad habits. It came to a point where he deflected the accusations and became defensive when Grimmi pointed out his hypocrisy.
She also started becoming frustrated with her mother for not standing up to her husband and his behavior. She was simply too busy trying to support the family, as she was the main breadwinner because her father couldn't keep a proper job. So whenever Grimmi pointed out her father's action, her mother would just sigh sadly and say nothing.
While they provided her with everything she needed, she started feeling like she was living a lie. They pretended to be a "good family" while they were splitting apart, only getting worse the more entitled her father became. It eventually turned into emotional neglect, where not even Grimmi would care for her own feelings, just choking them down and playing pretend. She believed it was easier to keep the peace than confront her father and cause an argument yet again. Just like her mother.

This all came crashing down in her first year of high school.
A group of delinquents found out about her quirk and starting including her in their group. Happy to finally have friends, Grimmi completely missed all the red flags, not realizing their true intentions. They hung out for weeks before they eventually invited her to their 'outings', which turned out to be a series of petty crimes. They wanted her to use her quirk to destroy any evidence of their actions, and for a little while, desperate to be accepted, she did. But as the petty crimes became more and more serious, from sneaking candy bars from convenience stores to full on home invasions, Grimmi started feeling a huge sense of guilt that even her parents noticed her change in behaviour.
Terrified of their potential disappointment in her, Grimmi told her "friends" she didn't want to use her quirk for them anymore. The delinquents didn't like that, saying she knew too much and that tattling would only get her in trouble as well. Grimmi didn't want to tattle, she just wanted to stop, not break the law anymore. However, the group didn't believe her and they started threatening her with violence and ruining her reputation in school even more than it already was.
Terrified of this change in attitude, Grimmi started running away, only to be chased down by the group. She was eventually cornered by their leader, a boy named Kei, who started getting aggressive with her. In fear and panic, all her stifled emotions of frustration, anger and distress exploded and she activated her quirk in self-defense, which engulfed and dissipated Kei, killing him.

When she realised what she had done, Grimmi freaked out. She ran away, refusing to go home and admit her actions, horrified and humiliated with what she had done. When she didn't return home that night, her parents claimed her as missing, getting the police to search for her. However she hid out behind some outside bins, using the darkness to hide her from the authorities, thinking they were coming to arrest her for what she had done. Too scared to stay in her hometown, she left it altogether, with nothing but the clothes she was wearing.
When more than a day went by and she was nowhere to be found, the police and her parents called Jaggers, a private detective with a quirk that could track others down using their blood, to find her. Using some of her blood found in the location where she had been attacked by Kei (unknown to the police), Jaggers confirmed it was hers and tracked the blood with the police following him.

He eventually found Grimmi in the next town over, hungry, dirty and wet from the rain, but refusing to go home. She begged him not to tell her parents, explaining to situation when he pushed her to. There was something different about Jaggers, and she knew he wouldn't be angry at her actions, so she admitted everything, including her family problems.
He listened. He reminded her that she was only 16, just about to end her first year of high school. She should go home, she wouldn't be in trouble, it was in self-defense. Grimmi cried, saying everybody was scared of her already before she had even done anything, there was no way she'd be accepted or even tolerated now. Jaggers insisted she go home, seeing how he had a job to do.
Grimmi refused, saying she'd just runaway again, she couldn't be with her parents anymore. She couldn't pretend anymore, what little control she had had shattered the second she killed Kei, she wouldn't be able to act as if nothing happened and her family would have to confront their problems or bury their heads further in the ground.
Grimmi couldn't cope with either.

Seeing how distressed and shattered Grimmi was, and knowing what hero society was like, Jaggers caved. He claimed to the police that the trail had gone cold, washed away by the rain, so he had no way of finding Grimmi now. Once the police had returned to her hometown, Jaggers collected Grimmi and brought her to Musutafu where he set her up with a small apartment and job there, working as a bin loader. Nobody asked questions, anybody who associates with Jaggers never asks questions. Grimmi appreciated that.

For the next two years, Jaggers helped her form a new identity, now officially going by Grimmi. He helped her finish her high school studies by homeschooling, so that she at least had that. He also helped her train and control her quirk, so she'd be able to protect herself without killing anyone, as that seemed to distress her. She also met Weirdo and his kids that appeared out of nowhere through the years. She has no real relation with Weirdo, but loves his kids and often babysits them.

As she turned eighteen, her love and admiration for heroes only grew. However, she started becoming skeptical of sidekicks and some of the lower ranking heroes.
Due to her past of being used and leeched off of, she saw anybody that used the stronger heroes as a stepping stool into the hero industry as morally corrupt and weak.
She started 'testing' new sidekicks and heroes. This is where her vigilante work starts.

Whenever a new hero or sidekick was announced, she'd research everything about them. Depending on her research, she'd either approve of him, excited to see their potential, or be highly skeptical of them, and desire to test them.
She searches for the newbies when they're out alone in hero attire, and use her move Darkness on them. Depending on how they react to the attack and how quickly they cave in to her taunts (generally demeaning them and acting all villain-y), Grimmi would decide if she likes them or not.
If they figure out her weakness and are able to get a punch against her, or at least always stand strong, never showing weakness or giving in, Grimmi could find it in herself to respect that about them, and let them go.
However, if they start flailing, cowering or generally not being heroic, giving into her taunts or showing similar weakness, she loses any potential respect and only further torments them, only stopping once the engulfing process starts. She never kills them, but makes sure they know she doesn't approve of them. That if they crumble so quickly when against her, they'll never be able to stand strong against actual threats.
By that point, a lot of those she tests retire almost immediately. Some of them do continue as heroes, but she makes sure to bad mouth them wherever she goes, calling them lazy, corrupt, pathetic or whatever else.

She's most intense about sidekicks for the top 10 heroes, as she sees top heroes as the best, and so any sidekicks they get should also be the best. Especially when it comes to Endeavor's. Seeing how he saved her when she was little, she holds him to a higher standard and refuses to believe he'd ever accept anybody below amazing into his agency. This mean that for the past six years, whenever he'd get a new sidekick, they'd all report some quirk that trapped them in darkness for five minutes while being taunted by a voice who eventually 'approved of them' and let them go.
Endeavor has been trying to capture this vigilante, but seeing how Grimmi isn't stupid enough to confront Endeavor directly, she's always sneaky and random about her attacks.

When she was twenty, after a couple years of her vigilante work and being something of a lesser known urban legend, she was approached by the Shie Hassaikai. Overhaul wanted to see what she was about, and was less than impressed. The feelings were mutual, Grimmi immediately disliking him and his attitude to her. Knowing they'd be able to mutually destroy each other, they decided to make a deal. If she stayed out of their business, they'd stay out hers, as a sort of hostile co-existence. Not wanting to bring Jaggers any problems, Grimmi agreed, knowing that the police had they eyes on them anyway.
She stopped seeing Weirdo and his kids around this time, as they moved away for the safety of the children.

Around the time when the Nomus started popping up, Grimmi was approached by the League of Villains to join them, but she flat out refused, as she hates villains. They argued over morality for a while, Shigaraki and Grimmi getting on each other's nerves endlessly, eventually coming to a similar deal as with Overhaul; if they leave her alone, she leaves them alone. Despite that, they occasionally lurked around her just to keep an eye on her actions and making sure she didn't do anything that would hinder them. Whenever Dabi was the one coming to check on her, Grimmi was ready to throw hands, even though she knew she had no chance of beating him. Once things started getting serious with their plans and the heroes, they stopped checking on her, and now Grimmi is bunking with Jaggers while the war is happening, too worried about her quirk accidentally killing someone to get involved. She only helps whenever Jaggers is out looking for trapped or lost civilians, who they then help get to safe zones.