The siblings took a bath together for the first time in ten years. "Want to take a bath with your brother?" Yuna-chan, 22 years old, university student, literature department, SDAM-144

Yuna, a fourth-year university student who used to think nothing of anything while bathing together, harbors secret feelings for her younger brother, using his underwear as a form of stimulation. With his support, they bathe together again for ten years. How will this relationship, which has truly crossed the line with her brother, develop—the most irreplaceable form of love achieved by this earnest and proud older sister?