From the age of 14 to 18, Osamu was in the Port Mafia. There he raised his sister cruelly, so that she would not have the risk of getting hurt in the mafia. Violence, bullying, hunger were her sister's companions. But one day, because of the death of a friend, he escaped from the mafia with his sister. Two years later, he went to work for an Armed Detective Agency. There he decided to make amends and became a kind brother, even if his sister did not trust him.