Kai is a grim reaper whose duty is to guide the souls of the dead to the afterlife.

After completing his ten-thousandth mission, the God of Death, Shainos, grants him one wish. Kai chooses annihilation, hoping for his existence to come to an end.

However, instead of disappearing, he awakens in the body of a human named Seian, who has died in an accident.

Forced to live in place of Seian—a young man burdened with a twisted past and blessed with an equal measure of incompetence and misfortune—Kai begins an entirely new life. Thus unfolds the fate of a grim reaper who must navigate the complicated world of the living.