The protagonist is, of course, a human living on Earth. It is believed that no life exists in space. However, in reality, beings similar to humans were born about 9 million years ago (about 2 million years before humans appeared on Earth). Currently, a world far more advanced than Earth flourishes on the lunar surface. However, it does not look prosperous like Earth does. This is because the lunar people primarily live underground, raising plants and livestock. Most homes are also built underground. A special barrier is placed on the surface of the moon, making its existence unknown to other planets. It is possible to observe other planets from the moon. In addition to humans, various creatures that do not exist on Earth also live there. Oxygen, water, radiation, extreme temperature differences, meteors, and gravity—the many challenges cited as reasons why humans cannot live there—have been solved through dizzying development and innovation (limited to within the barrier). Somewhere on the lunar surface, there is said to be the grand and beautifully shining court of the Selene family, which even lunar residents cannot see. Probably only those of that bloodline have ever seen it.