My Mother the Mermaid (2004)

Na-young works at a post office and is sick and tired of being around her shamefully unyielding mother and her pushover father who's excessively nice. The only thing that she can look forward to is her trip abroad in a few days. But one day, her father leaves home without any notice. Her mother doesn't care what happens to him and doesn't care to look for him. Na-young has no choice but to give up her dream trip abroad and to search for her father instead. Once she arrives at her parents' hometown, Na-young is shocked to meet someone she'd never expect, even in her dreams.

Unfortunately the movie My Mother the Mermaid is not yet available on HBO Max.