In the vast emptiness known as the World Ovary, two adjoining worlds float. They are known as Heaven and Hell. The worlds are connected by a gate. However, their atmospheres are suffused with substances known as Heaven Element and Hell Element. To inhabitants of the opposite world, these are poison, so there is little interaction between the worlds.
Sakura... the only angel who is unaffected by the Hell Element. He journeyed to Hell on queen Anastasia's orders to find the forbidden mirror that it was stolen by invaders from Hell, but...
Maybe it's because of Kuroha, Sakura's alter ego created by the forbidden mirror, or maybe it's for a different reason... Either way, his body can no longer withstand the Heaven Element, and so he is unable to return to Heaven.
This is Hell, the village of the rabbit tribe...