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.
