Ranmaru is Harada Tokio's right-hand man and formerly a member of the Harada Faction. But when Harada decided that he was getting too busy to maintain the group, he disbanded the faction, prompting Ranmaru to swear allegiance to Suzuran's Hana-Gumi.
Initially wasn't a fan of the faction's leader, Tsukishima Hana, but began to respect him after Hana himself visited Ranmaru during his mother's funeral and cried with him.
Ranmaru served as one of the Hana-Gumi's go-to men for information, as he has an extensive range of contacts to tap. He knows a lot of guys and, as such, is looked up to by many juniors.
However, he is also infamous for never smoking his own cigarettes and will be forever bumming smokes from anyone, including Kanbe Yoshikatu (a.k.a. Butcher) and the other members of the Hana-Gumi, much to their chagrin.