Eri, who lives in an ideal family, is cooled down by her boyfriend for the unreasonable reason of 'too intense sexual desire'. At such a time, Eri is revitalized by her younger brother 'Makun.' Then one day, when he sees a cock that has been created by him, Eri uses his real younger brother for sex processing because he can't put up with the frustrating impulse and says it is sex education.