Guinea Pig: Mermaid in the Manhole (1988)
Original title: ザ・ギニーピッグ マンホールの中の人魚
Guinea Pig: Mermaid in the Manhole is a 1988 Japanese-language horror movie directed by Hideshi Hino, with a running time of 58m. It stars Shigeru Saiki, Mari Somei and Go Riju.
An artist dealing with the grief of his wife leaving him finds solace in painting the squalor of the sewer. He discovers a trapped mermaid, whom he brings home to heal. Her condition worsens, and she asks the artist to paint her before she dies.