Abandoned by their mother when the younger brother was still a baby, Kihachi raised Yahiro practically single-handedly, sacrificing his own childhood and adolescence to provide for him. The two live together with an unreliable father, and Kihachi works multiple jobs to support them while Yahiro attends high school and plays on a sports team. Their bond is close and familial—until a friend of Yahiro's sends him a gay adult video, and Yahiro recognizes the man being penetrated on screen as his own brother, Kihachi.

Shocked and unable to sleep, Yahiro can no longer look Kihachi in the eye. Every act of care from his brother now carries an uncomfortable awareness. The story follows the emotional aftermath of that discovery as the brothers navigate a gradually shifting relationship. Yahiro begins to see Kihachi not only as a caretaker but as an individual with his own desires and vulnerabilities. Meanwhile, Kihachi has long been aware of his own feelings but has suppressed them out of a fierce protectiveness for Yahiro's future.

As the suppressed attraction grows into mutual romantic love, the conflict deepens: Kihachi, believing his presence is a hindrance to Yahiro's normal adolescence and eventual adulthood, decides the only way to truly protect his brother is to leave. The narrative explores the painful line between familial devotion and romantic attachment, culminating in Kihachi making the agonizing choice to separate from Yahiro for the sake of the younger brother's future happiness. The series is notable for its focus on the internal struggle of the older brother, his self-sacrificial love, and the gradual, inevitable recognition on both sides that their feelings have changed. A sequel series continues the story beyond this initial separation.