Monster Tinder

[Amaterasu]

Hiro Protagonist

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Wyvern!

Wyverns belong to the family of dragons and harpies, and in a way are the jack-of-both-trades between the two species as they sport the scales and physical strength of dragons as well as their intellect (though they are nowhere near as strong or resiliant as a full dragon) and the instinctual, primal side of harpies in addition to their wing-hands (but no regular arms in addition to that) and a relatively small, light body - though they lack the light frame and speed of harpies. Wyverns can thus risk falling to their own instincts (when hungry or tired, being scared of predator species etc.) and are more emotional and slightly more aggressive/abrasive than dragons. They are more intelligent than cliché "bird-brained" harpies however, capable of long-term thought and understanding large and complex problems, equivalent to an adult human.
As per his own explanation Hiro is someone who's intelligent and esoteric and who takes it upon himself to train so that he can save the world, but at the same time he's a lazy bastard and tends towards chaos - he understands the need for law and order but he dislikes an excess of control. Finally, he's a pragmatist - he's not above playing dirty to further his own goals, which is in line with his sort-of chaotic alignment. Ultimately though he fights for what's right - in his eyes, anyway.
Wyverns are, to put it bluntly, physical creatures. Because they are instinct-driven oftentimes and due to being part-reptile and part-bird, two creatures susceptible to cold temperatures, they need warmth. Hiro would be used as a human radiator many a time, especially in winter. Their aggressiveness means that the relationships they have are often controlling, though I doubt that Hiro would let Wyvern put him under her thumb(claw), in which case... well, it would be a relationship built on shaky pillars that can collapse easily and will need nurturing. I'm not going to sugarcoat it: Wyverns are a handful to handle and not everyone lines up with them. If Hiro wants to make it work he's got his work cut out for him. He'll deal with a girl that has a mind of her own and is certainly not afraid of butting heads, especially at the start of their relationship. Over time she'll warm up to him (though she may deny that!), but it's always going to be a relationship where disgreements will come up and will have to be resolved with compromises.
On the plus side? Wyvern's scales are not as sharp as those of a dragon and she's got four arms plus a tail to hug Hiro with, so physical contact will be comfy! And if he can introduce her to the wonders of modern-day TV and Internet, she'll have something to do when it's winter and she's in a semi-hibernating state wanting constant contact. Or when she's just having a lazy day. For these times, many an evening will be spent with literal (and eventually figurative?) Netflix & Chill.