Kunio Murai, the class "jock bully," isn't very intelligent and has a short temper. Upon Eikichi Onizuka's arrival at Holy Forest Academy, Kunio and his gang, which includes Kouji Fujiyoshi and Tadaaki Kusano, attempt to kill him through seemingly harmless pranks, like hiding a cockroach in his lunch. However, these plans backfire, with Kunio accidentally eating the cockroach instead, leading him to near madness, almost impaling his face on a pair of sharp scissors. Onizuka then exploits Kunio's 27-year-old mother, Julia Murai, after defeating Kunio at several arcade games. It is later revealed that Julia had Kunio when she was only 13, and her parents and boyfriend left her, making Kunio fiercely protective of his mother.
Despite their initial animosity, Kunio and his gang become friends with Onizuka after he saves them from a group of thugs. However, before this reconciliation, Onizuka joins the thugs and has Kunio bungee jump off the Tokyo Bay Bridge. Kunio remains highly agitated whenever Onizuka flirts with his mother, fearing that Onizuka might become his new stepfather. His anxiety about a potential new father escalates when he suspects his mother may marry a man resembling Dr. Elefun from Astro Boy.
