Masaru Kubo, a high school student at Ryouzuki, suffered severe boxing injuries during practice that plunged him into a coma. Awakening brought permanent physical limitations, ending his boxing career. Extended hospitalization led to insufficient school attendance, forcing him to repeat the academic year upon his return to Ryouzuki. Transferred out of the specialized sports class into general education, this demotion and the boxing prohibition left him deeply frustrated and emotionally adrift, as boxing had been his primary passion.

During rehabilitation, he connected with his classmate Ohse Yumiko. His relationships also involved Shouko Kubo, with whom he shared a past connection complicated by the aftermath of the match that injured him; Shouko harbored unresolved resentment towards his opponent, Yukinojou Yukimura, influencing their interactions.

After rehabilitation, Masaru spent time at a summerhouse with Saegusa Maki. Concurrently, he became indirectly involved in an incident concerning the kidnapping of Mizushima Akira when the perpetrators approached the summerhouse location.