Sakio grew up as a tiny but cute femboy, and for that, he was always bullied by his brother, who is taller, stronger, and smarter.

One night, due to an unknown phenomenon he turns into a girl, which he keeps a secret from others.
But little by little, people begin to notice something different about him and begin to take notice of his gender change.

And because he is such a weakling, he can't refuse when others ask him for sex– including his best friend, his classmates, his delinquent brother, and even his cute childhood friend, Michiru-chan (who grew a dick from her crotch).