Diamond

They want to be like Bort and tend to say odd things. Their hardness is 10.

Diamond is gentle and friendly to everyone.

They have a special type of fighting, where they use the sides of their sword to reflect the Lunarian's arrows.

While Phos tries to convince the gems to join them to the moon, Diamond confronts Phos and reveals their knowledge about Phos' facade. Diamond then agrees to go with Phos on the moon, with their inferiority complex towards Bort being the reason.

As a result of Diamond's hostility towards Bort, they are the first to attack upon seeing Bort in the raid against Kongou. Unfortunately, this ends up with both gems shattering eachother.