High school student Gamou Shouya is a dead man—sort of. The real Shouya Gamou has been gone for a long time, but his body survives, occupied by the soul of a boy who struck a deal with the succubus Armelina. In return for working as her personal hitman, Armelina assists him in tracking down those who brutally killed him and his family. The road ahead is dark and lethal, but Shouya has nothing left to lose... not even his soul.