Atsuo originally lived with his father. When the Five Deadly Shadows' minions came asking for protection money, he always defeated them. At last, the leaders of the Five Deadly Shadows offered a bargain to Atsuo: join them or they would killed all his family. Atsuo accepted and was trained by Namiko Li.
When rumors of the corruption reached the ears of the provincial governor in 1479 DR, she sent the magistrate Hiro Yun. Step by step, Hiro efficiently shut down all the gang's operations and arrested most of its members until only the five leaders remained. At this point, Hiro challenged the assassins but in the end was defeated. After Hiro's defeat, Atsuo decided to go back to his father to live simply as a farmer.
Later an adventuring party confronted and defeated him.
Atsuo became an assassin only to protect his family. However, he was quick to anger.