Yuuma Akiyama is a popular high schoolboy loved by the girls and hated by the average boy and is secretly an otaku at heart. After an unfortunate accident, he dies saving someone he cares about only to be reincarnated into a new world as a demon girl known as Nariko Helel ben Shachar.

In a world with no magic and where the only means of fighting the Forsaken are with Cipher-Frames, huge mecha powered by mana that flows through the universe. Nariko will soon come to the realization of the truth behind her reincarnation and her true purpose in this new world.