In a futuristic setting, a unique life form known as Houseki emerges. These 28 gems are tasked with battling the Tsukijin, who aim to imprison them as ornaments. Each gem is designated a specific function like combatant or healer. Despite longing to combat the lunar beings, Phos, an unassigned gem, is tasked by the gems' supervisor Kongo to edit a publication on natural history.