Tsuki to Mizu no Yoru(1997)

Tsuki to Mizu no Yoru

Meet the volatile Nakichi and peaceful Seita, the two water sprites that live in a river in the remote countryside. A chanced encounter with the human child Yoshiharu reawakens the half forgotten ties between water sprites and humans, and an amazing friendship is forged. Yet can this relationship survive the test when humans once again threaten the lives of these mythical beings?

(Source: Storm in Heaven)