「昔は一緒にお風呂入っても何にも思わなかったのに…」弟への秘めた想いを抱える大学4年生のゆなさんは弟の下着をオカズにしていた。そんな彼女を後押しして弟と10年ぶりの混浴へ。果たして弟との一線を越えた関係の行方は――真面目で自慢のお姉ちゃんが辿り着いた、いちばんイケナイ愛のかたち。
“In the past, we didn’t think anything of it when we took a bath together…” Yuna, a fourth-year university student with a secret feelings for her younger brother, used her younger brother’s underwear as material for masturbation. He supported her and went to a mixed bath with her younger brother for the first time in 10 years. What will happen to her relationship with her younger brother, which has crossed the line? The most unlucky form of love has been reached by her serious and proud older sister.

– JavGG.net