Kojou Akatsuki lives on the artificial island of Itogami, and he has a secret: He's the

Saito was reincarnated to the other world at the age of 15, becomes the Great Sage, and defeated the Demon Lord. Shortly after that, the door connecting the other world and the real world opens, and Saitou return to Japan with the power of the Great Sage.

Nanoka passes through a portal into the Taisho era, where exorcist Mao reluctantly rescues her from the jaws of a grotesque yokai. When Nanoka gets back to the present, she discovers she has some new, incredible abilities. She returns to the past looking