Sealed and forgotten below Tokyo, there is a world called Tokyo Underground. Bodyguard and element user Chelsea Rorec escapes the underground with the Maiden of Life, Ruri Sarasa. They take refuge in the home of Asagi Rumina but are soon attacked by members of the Company ordered to retrieve Ruri.

A boy opens a chest at his father's temple, and inside pops out a Hanyou, a half demon, half human girl who wishes for nothing more than to avenge the death of her mother, and her father by herself. It just so happens to be that the boy looks just like his ancestor, the one who killed the girl and mother.