Hakone-chan: Season 1

Based off of the manga Onsen Yosei Hakone-chan by Daisuke Yui, Hakone is about the hot spring spirit Hakone who descended to a spa resort on Earth. Due to her long slumber however, she now looks like a little girl.

High school boy Toya stumbles across her at a hot spring and ends up helping Hakone retrieving her original powers.