Once upon a time, many distant lunar kingdoms came together as one on Earth's moon. As a much more advanced society than ours, the majority of present-day human technology was originally developed by the people of the Lunar Gates hidden in the moon's atmosphere. Right underneath the palace are the six sectors, organized by occupational field.

Unbeknownst to us humans, peculiar beings roam the surface of the moon. Colloquially known as beasts, these diverse creatures possess a variety of abilities. They come in all shapes and sizes, sometimes encountered near towns and cities; though they primarily reside in the White Woods below.

When unruly beasts spiral out of control, it's up to the Beast Hunters to keep them in check. Endorsed by the royal family, this organization is in charge of cataloging all beasts in the known universe- and dealing with beast-related mishaps. Lumens and beasts lived happily together from then on.

In the present, however, a dark cloud looms over the Lunar Gates. This peace can't be kept for much longer...