In a strange future, crystalline beings known as Gems inhabit an Earth shattered by six meteors. Each Gem is assigned a job in the war against the Lunarians, a species that assaults them with the intent of shattering their bodies and using them as ornaments. Phosphophyllite, often known as Phos, is a youthful and frail Gem who want to assist their companions in the war effort. Because of their fragile health, they are instead instructed to construct an encyclopedia. Phos encounters Cinnabar, an intelligent gem that has been assigned to patrolling the remote island at night due to the corrosive poison their body produces, after reluctantly commencing on this assignment. Phos decides to discover a position that would make Cinnabar happy after seeing how miserable she is.