“It is that very frankness of yours that is needed for this task. I am counting on you.”
-Master Kongou to Phosphophyllite, Land of the Lustrous, Episode 1
In the first episode of Land of the Lustrous, Phosphophyllite is tasked with creating an encyclopedia for the gems. It becomes the catalyst for their transformation.. The purpose of the encyclopedia from a narrative perspective is to give Phos a push forward, and also to show how what they want to do (fight like the other gems) is at odds with what comes to them naturally due to their brittle 3.5 Mohs hardness. The encyclopedia leads Phos to Cinnabar, which in turn leads them to another self-assigned task of finding Cinnabar a new job. As soon as Phos begins to transform, the encyclopedia is all but forgotten.
However, the gems could really use an encyclopedia.