Shinobu Oda is the handsome and approachable first-year class representative at Asamizo High School. He shares a deep childhood bond with Nonoka Aida, a friendship stretching back to their earliest years. This connection is shadowed by a pivotal event eleven years prior: Shinobu intervened to protect Nonoka from a drunk attacker, shielding her physically and suffering a severe back injury. This injury caused permanent spinal damage, abruptly ending his "god-given" judo talent—a prodigious skill that had inspired others in the sport.

Forced away from judo, Shinobu redirected his focus towards academics and cultivated significant skill as a pianist. The assault left a prominent scar on his back, a constant physical reminder. Initially warm towards Nonoka, his demeanor shifts dramatically after she joins the school's judo club and grows closer to Yuuya Hashiba, the other boy involved in her rescue. Shinobu becomes cold and hostile, openly expressing disdain for judo and deliberately antagonizing club members, claiming amusement as his motive—a stance later revealed as deceptive. Despite this harsh exterior, underlying positive traits emerge, aligning him with the "Jerk with a Heart of Gold" trope; he gradually becomes less antagonistic and offers indirect support.

Shinobu harbors complex, persistent romantic feelings exclusively for Nonoka, exhibiting "Single-Target Sexuality." He explicitly declares, "I don't care about other girls. I only wanted you." Their interactions include moments of physical intimacy initiated by Shinobu, consistently depicted as forceful kisses that Nonoka explicitly states she cannot forgive.

His character develops further as he reconciles somewhat with Yuuya Hashiba. Their relationship evolves into "Vitriolic Best Buds," marked by sharp banter but underlying mutual respect. Shinobu plays a crucial role in the OVA climax: during Yuuya's pivotal judo match against Hajime Ichijou for Nonoka's freedom, Shinobu appears and strategically advises Yuuya on exploiting Hajime's vulnerability. This intervention enables Yuuya's victory, showcasing Shinobu's enduring tactical understanding of judo and willingness to collaborate despite their rivalry. Ultimately, he transitions into a supportive role for both Nonoka and Yuuya as they pursue Olympic-level judo competition.