SkunkyArt | JigsawArcobatic13 — Finn Mertens VS Arle Nadja

Both are young optimistic pure hearted adventure loving happy-go-lucky heroes from magical lands full of all kind of weird creatures where they go on adventures with their trusted helpful animal companion with great appetite and crazy powers (Jake and Carbuncle) when they for the most part look for treasures

Both are incredibly kind people that help whoever is in need, make a lot of friends from all kinds of people and creatures, even ones that were enemies and had even saved the world more than once. But despite that they aren't perfect (Finn had shown some time that he can be selfish or even come up as someone mean for some people while Arle have shown that she is really indispensable at time and to be quite mean or even come up as a jerk sometimes) although they become even better as people as their series progress

Both had fought an incompetent goofy romantically obsessed kings that are quite similar (Ice King and Satan) and foils a lot of plans although they had got friendlier with them as time go on and had even work together to stop a big evil that was threatening their world

At one of their adventures, both had found a really powerful legendary item (Enchiridion and Phantom Orb) after what was pretty much a big test for them to see if they deserve it. But both ended up refusing to keep it with them (Finn for giving if to someone who he believed needs it more and Arle for believing that the Phantom Orb is so powerful for any one to use it)

Both have traveled to different dimensions and even saved all of existence at some point

Both had participated in tournaments before (The tournament of 15th anniversary and Wizard Tournament)

Both had fought an eldritch cosmic creature with the ability of corrupting and possessing other creatures (Lich and Yog-Sothoth)

It was a plot point in both series when a powerful knowledgeable hero was possessed by a sinister entity that take advantage of possessing them to manipulate a young hero into gathering certain things from across the land before those sinister entities revealed themselves to be cosmic beings that want to end everything (Ecolo and Lich), interestingly both Arle and Finn had opposite roles in that event when Arle was the one possessed while Finn was the one manipulated

Both once had an adventure just to find food ingredients (Finn going in an adventure to find Tree Trunks appels for her to make an apple pie for him and Jake and Arle having an adventure in one of the side game just to buy ingredients to make curry for her and Carbuncle)

Both had a doppelganger of them (Doppelganger Arle and Fern) that came out of them (Doppelganger Arle is Arle's other half and Fern born out of Finn's two swords) and believed themselves to be the original which lead to conflict against their main counterparts

Both were revealed to be the reincarnation of a powerful being in their universe (Lilith and the Catalyst Comet) [I should point out that Arle being Lilith reincarnation is an information from the likely non canon Shin Madou Monogatari, I only included it because stuff from Shin Madou Monogatari are already included in most of her matchups]