Teased unmercifully for his past as an orphan and a slave, Teito has only his best friend Mikage to ease his days at the elite Barsburg Academy - and his mastery of the magical art of Zaiphon! But even that will not be enough to save him when he discovers a horrifying secret behind the ruling Empire. Trapped in an ancient battle between a wicked Death God and the Seven Ghosts and guided by three mysterious priests, Teito discovers a power that could save the world... and shed light on his own mysterious past.

Kokuryuu Kaguya was only a little boy when he witnessed his father murdered by demons. He spent years trying to convince people about what he witnessed, but was dismissed as a traumatized child with an over-active imagination. Now a teenager, Kaguya still remembers what happened.

One day, Kaguya is struck by a mysterious light and meets a young girl named Mao—a skillful warrior wearing bunny ears—who rescues him from a demons' attack, then demands to know what planet he's from! Kaguya finds himself inducted into a secret organization of other-worldly individuals whose goal is to defend Earth from monstrous invaders. Reborn as a Battle Rabbit, strange powers awaken within Kaguya which allow him to fight these creatures and seek vengeance for his father's death.