Besides the fact that Izaya was born a pure-bred demon, we know very little about his past. He grew up in Tokyo, Japan and has revealed he has two younger sisters. Anything else still remains a mystery.
Izaya will openly admit that he is at Spirit High for his own selfish reasons, he wishes only to toy with people with the benifit of his own personal gain. He is unfortunately realizing he has almost zero asperations and is trying to change his way of thinking. But force of habit, and his demon blood wont let him do this easily. He has made few friends, and his own loyalty is somewhat questionable.
- demonic possesion. when it comes to mortals Izaya can gain full power over the actions of the body in possesion, however when possesing another supernatural being he is unable to control their abilities, as in they won't function under izaya's control. only their bodies. unfortunately, Izaya is easily excersized from a host with enough mental objection.
- mind reading. Izaya himself considers mind-reading a cheat, and barely ever uses it on others. instead he relies on manipulating the people around him for his own personal amusement.
- coercion and subversion. again, izaya almost relies on his talents having to do with manipulation. and as a result is highly destructive in complex ways. life is a game and we are all pawns.
- soul eating. well... that was before he became a vampire. xD
- becomes more powerful the closer he is to death. also, he's relentless and stuborn, probably best to just leave him alone - try to be passive with izaya as much as you can.
- bloodlust. after being bitten izaya's soul eating was transformed, his insasiable hunger towards eating the souls of others was replaced with bloodlust.
*pease note that i intent to irradicate izaya's vampireism eventually as a plot device.