Pyotr Ilyich Tchaikovsky

Tchaikovsky is one of the nine members in class S-. He has a habit of testing people's strength by grabbing their wrists in one hand and telling them to escape.

It is later revealed that he used to have a girlfriend in Russia whom he loved, but was dumped by. Ren is the only one who could make his heart race after that incident, and his behaviour indicates that also he knows about Ren's gender.