Ningyohime Marina no Bouken (TV Series, 26 episodes, AniDB)

Requested on Sept. 25, 2021, 3:03 p.m.

Marina, a lonely mermaid, is bored of underwater life. She wants legs. She goes to the sea witch. She is given a magic whistle that when blown, can turn her into a human or mermaid. The Prince and Marina fall in love but she can`t stay with him until she can get the sea witch off her case. Source: ANN