TLDR, Zaiyu is an Estil, an elven species of humanoid aliens. He's technically digitigrade, walking on his toes rather than his full foot, and his movements are all subtly off from what a human might expect--especially when he's on the ground, as Estil are a flying species and being ground-bound is weird and annoying to him. He has pointed ears, eyes that glow a single solid green colour, retractible claws on his hands and feet, and is covered in a rainbow of shifting tattoos that mark his mastery of every field of magic (except necromancy, which he was never taught). His hair is also cut quite short, which only matters to people who have realized that his hair is essentially mobile sensory tendrils, so wearing it in a bob cut is an act of self-mutilation. He also has cute little fangs and his right arm is currently made of immobile white crystal from about halfway down the bicep. The current of mana within his body is faintly visible within the crystal. So, yeah, Zaiyu is clearly not human, but in such a way that a dedicated cosplayer could theoretically steal his look (except for the moving hair, which might be a little harder to copy).
Sasori, meanwhile, is a whole other ball game. Not only is Sasori much more obviously digitigrade than Zaiyu, he's much bigger in general, standing about 6'6'' on the rare occasions that he actually holds himself up straight. His anatomy is a mash of various creatures he copied traits from mixed with an overall humanoid body plan--or, more accurately, an overall Estil body plan--and the result is very uncanny. He has horns, shark teeth, an intimidating armoured carapace, disproportionately large big cat claws, a massive scorpion tail, a natural 'cloak' of fur around his shoulders, an array of venomous spines, and shifting stripy markings that break up his outline a little. He tends to move in a predatory hunch, drops to all fours when agitated or trying to get comfortable, and his colouring is all wrong for either human or Estil. By which I mean, he has blue skin, lighter blue hair and armour, and glowing red eyes with black sclera. Anyone looking at Sasori is likely to be struck with a sudden and visceral sense of wrongness, especially if they know how a human or an Estil is supposed to look and can tell how off his proportions and body language are.
Both of them also have pretty feline body language and habits, hence me calling them catboys even though they have a lot of other stuff going on.
