Kotone, a cute girl of marriageable age, has a hopeless perverted brother who is always hiding in her house, spying on her masturbating or bringing her boyfriend over for sex. One day, he sneaks into Kotone's room to try and have sex with her at night, but is caught. From that day on, the brother becomes his sister's slave, and it seems that his sister is forcing him to perform cunnilingus on her as a daily routine... There's blood...