Character A has always had a fascination with the creepy and unusual. They collect things that are creepy or unusual, such as animal bones they might find, animals with weird illnesses, such as two-headed snakes, and anything else they might find. This is all very hidden though, they live a normal life outside of that, has friends, goes to uni/has a steady job, all in all, to anyone outside, they seem just like anyone else. But when they see the other character, someone so strange, a cryptid, something nobody, including themself, believed to exist, they realized they must have character b.
Meanwhile, character b is a creature of fables, somehow existing in this normal world. They had to learn to hide themself, being seen by others as a monster. So when a person, an actual human, seems to like them, view them as something other that a threat, a danger, a monster, they trust them too easily. B enjoys finally being able to exist around people, or, rather, a person. They lower their guard.
And character a strikes.
If at all possible, I'd like character b.