Minami-kun no Koibito - My Little Lover

Shunichi Minami possesses good looks and does well academically in high school. Chiyomi Horikiri is a bright girl who likes dancing. They were childhood friends and also their first loves, but after Shunichi Minami’s father disappeared they hardly talk. On a stormy night, Chiyomi Horikiri has an argument with her parents over her future plans and leaves home. While trying to avoid the rain, Chiyomi Horikiri wishes that she could go back to her childhood. Suddenly, Chiyomi becomes 15 cm. tall. Shunichi Minami happens to see tiny Chiyomi Horikiri. She tells him that she doesn't want anyone else to see her and Shunichi Minami takes her to his home.
~~ Adapted from the manga “Minami-kun no Koibito” (南くんの恋人) by Uchida Shungiku (内田春菊).