Chuuya is a detective in the Armed Detective Agency, but back then he used to be in the Port Mafia. When he was sixteen, almost seventeen, he left and joined the ADA. In the Mafia he used to be partners with Dazai, their past was complicated, they were the most feared dou, the Double Black. They argued a lot, but they were the strongest. Sometimes they even had some peaceful moments together. But after Chuuya left Dazai became the next boss of the Port Mafia.