Kono Kankei wa Gouhou desu!

YES Sister, NO Touch! Kouta, who is an extreme sis-con, decides to move out and live alone in order to "escape from his little sister." One day, however, he picks up a runaway girl named Ui, who clings to him and acts just like a little sister. Although she looks and acts like a child, she is in fact a beautiful 19-year-old girl with big tits! Protect this girl like a real sister? Or dare he cross the line? The days of agony begin! (Source: Kodansha, translated) Note: Original serialization ran for 22 chapters. In the volume release, Chapters 21 and 22 were combined as Chapter 21.