Ai Coleman used to be a quiet and withdrawn boy from Hole. He was raised by his grandfather, and was neglected by him. But Ai was a very intelligent kid, and the absence of stimulation in his life left him quite bored and depressed. He spent his time reading books. Or at least one about sorcerers written by Dr. Kasukabe. Ai hated living in Hole, and he hated that sorcerers came there to experiment on humans, but he was also fascinated by them. And so, Ai decided he'd find a way to become a magic user. Though Dr. Kasukabe tried to dissuade him, claiming it was impossible for a human to become a sorcerer, Ai was more clever. He figured out a way to incorporate powers from sorcerers by undergoing dangerous surgeries and experimenting on himself. Using these methods, Ai amassed a vast amount of power and left a trail of carnage in his wake. He surpassed the strongest sorcerers and set his sights even higher - to become like the Devils who rule over the sorcerers, and perhaps to surpass them too.

Spoiler

For most of the story Ai lived in a dimensional distortion inside "Kaiman," which was a kind of microcosm of Hole. He appeared as a boy who was missing the top half of his body and spoke with gurgling "splosh" noises coming from his exposed entrails. Ai very rarely left this dimensional distortion because his outer body was a zombie after having died and been revived on Living Dead Day. Instead, he exerted his influence from within by managing the multiple heads and spare body parts of his other personalities.