He is an old friend of Yoshino's, and is her adopted relative. He was abandoned by his biological father in middle school, and became an orphan. He was then adopted by Yoshino's grandfather Somei Renji who is the boss of a Yakuza organization in Osaka. Currently he's a university student and Yakuza. 

★|Your brother's best friend

Nagumo is an old friend of Taro Sakamoto and a member of The Order, making him one of the strongest assassins in the JAA. He's a bad boy.