Kai has a demonic spirit sealed deep within his body. It's name? Rekikotsu. It usualy lays dorment inside of him, but under extreme conditions, or during one of his psychotic meltdowns, the demon's influence can be physically seen on Kai. He loses even more of his sanity (if there's much more to lose), and does anything unpredictable. The references for his design are pretty obvious to anybody into anime and rpgs. The majority of his dark look is based off of the Heartless from Kingdom Hearts, and Kai's ponytail's transformation was inspired blindly by Midna from Legend of Zelda: Twilight Princess (I realized where I got the idea from as I was scanning it XP) The demon within concept is based off of Naruto, since Kai was a Naruto rp character longer than anything else. He actualy looked a lot different than this in oroginal design, but it never quite fit him. Rekikotsu often actualy appears in a "pure" form, a little boy Kai named Reki. Reki isn't evil at all, and is fully aware of the darkness inside of him. He's sort of a ghost, and.....well, I'll explain more about him some other time (Like when I draw the newer version of him )