The Houseki fight against the Moon Dwellers, beings who attack them and use their shattered bodies as decorations. Each Houseki is assigned a role, and Phos, the youngest, is assigned to create an encyclopedia of natural history.

In the distant future, a new immortal and genderless life form called Gems populate the Earth. The 28 Gems must fight against the Lunarians, who attack them regularly to abduct them and to turn them into decorations. Each Gem is assigned a role, such as a fighter or a medic. Being only 300 years old, Phosphophyllite is the youngest of the Gems and has no assignment yet. They want to help to fight the Moon Dwellers, but are too weak and brittle for battle. One day the master of Gems, Kongou (Adamantine), assigns them the task of creating a natural history encyclopedia.