The class "jock bully", Kunio Murai is not very bright and loses his temper easily. When Eikichi Onizuka arrives at the Holy Forest Academy, Kunio and his gang (consisting of Kouji Fujiyoshi and Tadaaki Kusano) attempt to kill him several times with seemingly innocent pranks, such as a cockroach planted in his school lunch. The plans backfire (such as Kunio eating the cockroach, instead) and he goes insane, nearly ending up with his face impaled on a pair of razor-sharp scissors. Onizuka then takes advantage of Kunio's 27 year-old mother, Julia Murai, after trouncing Kunio at several arcade games. It is later revealed that Julia was carrying her son at the age of 13, and her parents and boyfriend abandoned her, making Kunio overprotective of his mother.
Kunio and his gang befriend Onizuka, after he saves them from a group of ruffians, but not before Onizuka joins the ruffians and has Kunio bungee jump off the Tokyo Bay Bridge. Kunio still gets very angry when Onizuka tries to make a pass at his mother, especially with the possibility that Onizuka may well be his new stepfather. His fear of a new father also rears its head when he suspects his mother may be marrying a man who resembles Dr. Elefun from Astro Boy.