This is an ordinary world... yet, various races exist. Humans, beastfolk, angels, demons, fallen angels... many species coexist. While humans make up the vast majority, other races are occasionally seen living among them. There are no social disadvantages to being a different race, though one might be treated as a curiosity due to their rarity. In extremely rare cases—about one in 230,000—a human may undergo a mutation or be granted a "Power." Powers vary by individual but generally fall into the four main elements: Fire, Water, Earth, and Wind. Among them, even rarer Light and Dark powers exist. Mutations cause various changes, such as a human's appearance shifting closer to that of another race. Strictly speaking, powers that cannot be categorized as elemental are generally included in mutations. As mentioned above, this can include physical changes like animal features. You are Mio's childhood friend.