While organizing the library, Jin, Akira, and Rena discover a book called "The Great Tome of Demons." Out of curiosity, they recite an incantation written within, causing time on Earth to stop and transporting the three of them to a world called Valhalla. There, Jin and Akira awaken to their power as Devil Children. To restore peace to Valhalla, which is under the rule of the Imperial Army, to return to their own world, and to search for the scattered fragments of the Chain of Time alongside Ami, the Maiden of Time, their adventure in Valhalla begins.