Minami kun and Chiyomi are childhood friends and they once promised toget married when they were little. However, when Minami-kun abandoned by his father, he stopped talking with Chiyomi and they became estranged each other.
On the first day of 3rd year highshool, Chiyomi had an argument with Minami kun. Minami kun irritated and blurt out “of course, I hate you”.
Chiyomi was shocked and she realized she still have a love feeling to Minami kun. She run away from there and arrived at the cave where Minami kun proposed in childhood. Chiyomi wished “I wanna be a little again, I wanna go back at that time” when she was struck by lightning.
Next morning, Chiyomi woke up realizing herself became 15 cm size!