この関係は合法です！

はいお姉さん、ノータッチ!?Yes sister, no touch!? Kouta, who is an extreme siscon, decides to live alone with the aim of "de-sister". However, one day, he picks up Ui, a runaway girl full of sister feelings. She has a young face and behavior, but she was actually a 19-year-old busty beautiful girl! protect her sister? Will you cross the line!? The days of agony begin!