|Title||Kokuyou Junior High Delinquent|
|Manga Debut||Hidden Bullet: Mukuro's Illusion|
Yaginuma (柳沼, Yaginuma) is a character who only appeared in the first volume of Reborn! Hidden Bullet novel series: Mukuro's illusion. He was a delinquent at Kokuyo Middle School.
When Mukuro, Ken, and Chikusa transferred into Kokuyo, Yaginuma and his gang decided to challenge them when he heard that they had made a lot of trouble in their old school overseas, but Yaginuma's gang was quickly defeated by Lancia (who was posing as Mukuro), Ken, and Chikusa. After his defeat, he told one of his schoolmates, Masato Hitsuji, that he would follow Mukuro, now knowing how dangerous he is and suggests for Masato to do the same. When Masato refused because he wished to change the school, Yaginuma called him a worm for still doing pointless things, leading Masato to attack him in anger and eventually resort to violence. Mukuro used this as an opportunity to place an illusion on Masato that made him believe that Masato had changed the school to a much better place within a week, while secretly using violence on Yaginuma and his gang when they misbehaved to keep order of the school.
However, Masato then heard that Mukuro and his gang had returned and decided to confront him, but like everyone else, was immediately defeated. When Masato awoke, he found Yaginuma and his gang unconscious not far from him and only three days had passed. Mukuro revealed that everything Masato saw and experienced had been nothing but an illusion and nothing had changed except the fact that Masato did use violence on Yaginuma and his gang. Mukuro undid the illusion he had placed on Yaginuma and his gang that also returned their memories of what Masato had done, leaving Masato to be beaten up by them. What happened to Yaginuma afterwards is unknown, though it can be presumed that he and his gang follow Mukuro.