Houseki no Kuni

In the distant future, a new immortal and genderless life form called Gems populate the Earth. The 28 Gems must fight against the Moon Dwellers, who attack them regularly to abduct them and to turn them into decorations. Being only 300 years old, Phosphophyllite is the youngest of the Gems and has no assignment yet. They wants to help to fight the Moon Dwellers, but is too weak and brittle for battle. They find their calling when the master of Gems assigns they the task of creating a natural history encyclopedia.