Onsen Yousei Hakone-chan(2012)

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. The high school boy Touya stumbles across her at a hot spring and ends up joining Hakone in retrieving her original powers.

(Source: Anime News Network)