D.Gray-man is the story of Allen Walker, who roams a fictional 19th-century Earth in search of Innocence, a mysterious substance used to fight demons known as akuma.

Allen Walker continues the tale of his past as an orphan child working in a circus. He was called Redarm then and knew little but misery in that life. He did, however, befriend one of the clowns, Campbell, and his dog, Allen. Another clown, Cosmo, hated both Campbell and Redarm and performed a dispicable act in order to torment them. Meanwhile, Allen's future master, Cross Marion, was finally reaching the end of a long hunt for a most elusive quarry.