The head of the police department anti-phantom thief bureau. He despises Joker and tries his best to capture him. However, his attempts always backfire on him. Oniyama is completely dedicated to capturing Joker and locking him up. Almost always he will be present at the scene of the crime, waiting to finally capture Joker. However, in dire situations, he will begrudgingly work together with Joker. He also cares for his family very much.