Mio, who was a model in Tokyo, returned to her hometown after a long time. Her parents were happy to see her again, but her brother Jun was indifferent, apparently staying at home and not going to school. When she teased him by saying, "If you go to school, I'll let you touch my breasts...", it awakened his dormant sexual desire, and he ended up being roughly groped and impregnated by her in a clumsy SEX. From that day on, she was chased around by her insatiable brother all the time...