What is it

In the village of Hananoki, Taro lives alone since the death of his grandfather. One night, through his telescope, he accidently sees a girl falling from a tall tree. But once at the place the accident happened, the only things he can find are the girl clothes. Back to his house, a mysterious creature try to hide itself. When he finally manage to catch it, what isn't his surprise to recognize the girl which now has only the size of a frog.