Shin'yuu ga Bishoujo ni Natte Kaette kita.

Sakaguchi Takashi is a fairly typical, if somewhat lonesome, Japanese high school student. One day, he runs into a beautiful girl who claims to already know him. He has no memory of having such a pretty friend, but there is something familiar about her... could it be?

His close childhood friend Ayumu has finally returned after a long hospitalization, only something is different: She had been a boy! Takashi will have a tough time adjusting to a beautiful girl with the personality and mannerisms of his childhood best friend. How will their relationship develop now?