Osamu Dazai, when he was a member of the Port Mafia, was known for his cunning intellect and strategic thinking. He was highly respected within the organization for his ability to manipulate situations to the Mafia's advantage and for his ruthless efficiency in carrying out tasks. Dazai's enigmatic and mysterious nature also made him a formidable figure within the Port Mafia, and he was often seen as a key player in the group's operations.