**Hardness:** Unknown
Kongou is the teacher of the lustrous. He has a vast amount of knowledge and has the power to drive away the Lunarians with a single attack.
Normally, Kongou is quiet and stoic. When he speaks, he is straightforward and concise. He only rarely displays emotions, but this is rumored to be because he is deliberately hiding them and that his face would be very easy to read otherwise. On the rare occasions where he shows humor, he is still as deadpan as ever. Kongou cares for the Gems considerably and blames himself when they are injured or taken away by the Lunarians.
