In the World of Dorohedoro, there is a split division of people who can and cannot use Magic.
The plot centers around Kaiman, who does not remember who he was before he was transfigured by a Magic user. This transformation left him with a reptile's head, and a desire to find out the truth about who he really is. Accompanied by Nikaido, his female companion, he tracks down Magic Users in The Hole and unceremoniously chomps down on their head, hoping to find out who it was that put him in this state.