Blame Hecate for this one...
Demota is the demon that comes with Aimi's magic make-up. I think he's actually the keeper of the make-up, but its very much the same thing. He met, ok accosted, Aimi one day and forced her to transform. Suffice it to say that they've been living together ever since.
Demo considers Aimi to be his older sister, and she returns the sentiments. Both of them were lonely and found that they could make a family for one another. Its all very sweet.
Demota has two forms: 10 year old boy with funky hair and little bat-demon. In both forms he speaks with a terrible lisp. He's also something of a pervert. Other than that, though, he's a fun little guy and very devoted to his "sister".