Monster Tinder

[Amaterasu]

Guu

[spoiler]

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Dullahan!

Guu was one of the slightly more difficult ones because she doesn't seem like the sort of person that gets emotionally attached to someone - as in, genuinely attached. Haré, from what I heard, was more of a victim and a sort-of-but-not-really friend who had to endure her troll-ness and antics. She's not an unfriendly person but she needs someone who, while not completely ignoring that part of her, will take it. And they should be older than a kid, someone mature enough to grow emotionally attached beyond a simple friendship.
Dullahan will be that person. Yes, I know that the image is of a headless horseman with a jack-o-lantern head, leave me alone. I'm trying to paint a character here.
Dullahans, for those unfamiliar with them, are a type of supernatural spirit. While not Grim Reapers themselves, they have their roles before and after a person's death: it is said that they splash someone doomed to die soon with a bucket of blood, and that after their death they guide the soul over the Sanzu River to the afterlife. Some Dullahans are capable of influencing a person's fate however, to prolong or shorten their life. They could guide a person back from the brink of death or kill them on the spot using their weapon of choice, which tends to be an executioner's sword or a scythe.
It's likely that upon meeting him Guu would troll Dullahan for a while by stealing his head and replacing it with a jack-o-lantern or some such, with the best part being that he would not even notice for a while: his body, for lack of eyes, is blind and whatever he puts on his neck would gain the properties of a head. Until he encounters a mirror or finds that his head is oddly round and smells of pumpkin, Dullahan would be none the wiser - and rather quite enraged and embarassed when he finds out. Not that he could do much to Guu, with her being a supernatural deity and whatnot in her homeworld, and a Prime in the Omniverse. Not even Dullahan can permanently kill a Prime. And considering his nature as a spirit beyond life and death he may very well attempt so with Guu for no reason other than that she messed with him.
Dullahans are a serious bunch, and this one's no exception. Emphasis on serious: he's not stoic. Guu's antics and her failure to take him seriously would annoy him and the fact that she's so resistant to his supposedly absolute powers would cause his pride to feel hurt, meaning that while he would react to Guu's pranks and tricks he would not just leave her. He'd try to kill her in her sleep, sure. But at best that would just buy him seven days of peace.
Will the relationship evolve beyond that? Given enough time, yes. If Guu is patient with Dullahan, he's going to start seeing beyond the prankster that Guu is on the surface and discover her caring side. That she does this sort of thing not to anyone, but to people she cares about. And that she didn't give him his head back and tell him to gtfo because she enjoys his company. And his attempts at killing her might become rarer and more half-hearted. Guu on the other hand would have someone that she can show her real self to more, without being as cautious as she really is: an eldritch creature drives people to insanity with its mere presence, after all, but Dullahan's not people. If she musters the patience for it, this very peculiar relationship will turn into a good friendship and more than that eventually. It's just going to be a shaky start, and far from guaranteed to work out. But then again, what would be the fun if everything went smooth as butter?