Land of the Lustrous is set in a far, distant future where the Earth had been struck six times by meteorites, ravaging it in the process. All of the remaining land was reduced to a single coast, whereas nearly all life was destroyed. Over vast stretches of time, a new race of sentient lifeforms emerged; immortal jewels that take the form of people. Phosphophyllite (Phos) is weak (with one of the lowest hardnesses) and considered useless by their peers. Phos asks their aloof but wise colleague Cinnabar for help after they receive an assignment to create a natural history encyclopedia, thus beginning their friendship and personal growth. Meanwhile, the lustrous are at war with the Lunarians who want to take advantage of their luxury value.