Ōba leads a rival group from Marutake High School, instantly recognizable by their red mohawk hairstyles evoking the Leningrad Cowboys. His gang persistently pursues confrontations with Kenji and his friends, driven by Kenji's fearsome reputation. However, these encounters stem from misunderstandings; Kenji's mere presence inadvertently triggers Ōba's followers to retreat without any violence. Ōba perceives Kenji's avoidance of a planned fight as a deep personal insult, intensifying his resolve to retaliate and prove dominance.

To force this confrontation, Ōba and his gang lie in wait for an ambush in a parking lot. This plan derails when bystanders mistake Ōba for a shift worker, resulting in him being forcibly transported to a fish-canning plant for employment. Despite this setback, Ōba remains singularly focused on challenging Kenji. This fixation culminates in a direct encounter just before a local rock festival, where Kenji unexpectedly smashes his bass guitar and plays a recorder, leaving Ōba stunned into silence.

Ōba and his gang subsequently follow Kenji to the festival venue. There, they witness Kenji's band, Kobujutsu, perform alongside Morita's group, Kobijitsu. The performance captivates the audience, including Ōba, who watches the entire event in silent disbelief, making no further attempts at intervention or conflict. Ōba's mature voice casting, contrasting with his teenage status, lends his character an authoritative gravitas against his youthful gang motivations.