Onsen Yousei Hakone-chan

The story follows Hakone, a hot spring spirit who descended to a spa resort on Earth. However, with her long slumber, she looks like a little girl on the outside. ("Yōsei" in the title is a wordplay on the Japanese words for fairy and a young child.) The high school boy Tōya stumbles across her at a hot spring and ends up joining Hakone in retrieving her original powers.