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. The place is Heaven. The "forbidden mirror" has been stolen by invaders from Hell. Queen Anastasia summons Sakura, who is the only angel who isn't affected by the Hell Element, and commands him to retrieve the mirror. However... Source: The Developer Website.