Izetsuki Orihara is the vampire version of Orihara Izaya. He was human, but became a vampire many centuries ago. This alternate of Izaya was created around Halloween time.
Izetsuki, in terms of personality, is much like Orihara Izaya. His love for humans, however, is a bit more intense than Izaya's since he can follow someone from the day they're born up to the day they die, giving him the opportunity to play with a person's life and experiment as much as possible until he either gets bored or the person dies.
He enjoys having eternal life and in no way gets bored with it, feeling indifferent towards his condition as a monster and easily forgetting that he's not actually human because the actions he takes feels natural to him. The only time he actually feels bad about not being human is when Pritzuo reminds him that he's a monster.
Izetsuki was originally a human many centuries ago who was later turned into a vampire. The vampire who turned him abandoned Izetsuki immediately afterwards, so Izetsuki never knew his mentor, nor did he cared enough to look for him. The original shock of becoming a vampire made him refuse to feed until he could no longer resist the urge. Throughout the centuries of his existence, he has since then adapted to being an immortal monster.
Izetsuki's hate for Pritzuo comes from his ability to make Izetsuki dislike his own existence. Even knowing it is an irrational feeling; Izetsuki can't avoid it and constantly shows his vampire abilities around Pritzuo just to oppose this feeling.
(For more information, check Pritzuo's page.)