The parents of the protagonist are traveling abroad to celebrate their 25th anniversary, the protagonist and cute sister, Izumi, are left alone however, the sister receives a phone call, her mothers is ill and she should go to give a hand.
One problem however, Izumi had to go to the university no matter what, she was just admitted after all, she must attend the school opening..."Could you go for me instead big brother"... but the university is a garden exclusively of girls, its an all girls university...how can he sneak in and go to classes instead of her sister? .... will he go as a woman?
