College student 'Ayumi' calls her boyfriend 'Kenji' home while her parents are traveling. Then, he starts having sex with her younger brother 'Ma-kun' so that he doesn't notice, but he is caught on the way, and Ma-kun misunderstands that her older sister is being bullied because he has no knowledge of sexuality. In order to tell the truth about her to her precious younger brother, Ayumi put her body on her own and performed sex education.
