Ōta ranks among three high school delinquents feared in his town, known primarily for his place in Kenji's group. His pompadour hairstyle fits the common Japanese delinquent look. Alongside Kenji and Asakura, Ōta spends considerable time loitering, skipping schoolwork, and engaging in minor troublemaking, though their violent reputation outstrips their actual deeds. Their routine involves playing old computer games, sitting in shared silence, and wandering aimlessly, often until janitors need to lock school facilities.

He joins Kenji's impulsive decision to form a band after Kenji gets a bass guitar. Following Kenji's lead, Ōta helps steal instruments from the school music room. This theft results in an unconventional band setup: two bass guitars, one played by Ōta, and minimal drums. Without musical experience or technical skill, Ōta strums his bass mechanically, contributing to the band's raw, rhythmic, and discordant noise. Despite the lack of melody or conventional ability, he finds deep personal satisfaction during early jam sessions, visibly affected by the physical act of making noise with his friends.

When Kenji abruptly declares boredom and disbands the group just before a scheduled festival gig, Ōta shows quiet resolve. He continues practicing with Asakura, expressing confidence Kenji will eventually show. This persistence contrasts Kenji's apathy and highlights Ōta's unspoken commitment. During the festival, he initially freezes onstage without Kenji but starts playing once Kenji arrives unexpectedly. Ōta participates in the climactic performance where the band merges with Morita's group, creating a cathartic, collaborative sound. His usual stoic expression breaks momentarily, revealing intense focus.

Ōta's interactions demonstrate loyalty and simple acceptance. He backs Kenji's spontaneous decisions without question, whether pursuing fights or music. His relationship with classmate Aya involves casual, non-romantic banter, including asking her to go to Disneyland. After the festival, Ōta sees Kenji and Aya talking alone but deliberately avoids interrupting. He later suggests reuniting the band to Asakura, showing his preference for maintaining the group's dynamic despite its instability.

Physically imposing yet intellectually uncomplicated, Ōta communicates sparingly through terse statements or gestures. His expressions remain mostly impassive, creating deadpan comedic moments. He embodies the film's theme of amateur creativity, finding value in unstructured expression without concern for outside judgment or technical skill.