"I became a girl." Takumi Musashino is a male student who suffers from a mysterious illness of unknown origin. Gene therapy saved his life, but his body was transformed into that of a woman! When Takumi, dressed in cute clothes, shows off to his male classmates, they become aroused by his appearance...!? "Girls' Day" Having lost her virginity, Takumi awakens to the pleasures of being a woman. Takumi was shocked to find his fingers covered in blood after he came from masturbating! Anri, who rides the train to school with me, tells me she's on her period and that she's become a real girl. But at that moment, the man's hand went to Anri's crotch... The man also extends his evil reach to Takumi, who tries to help Anri...!?