Takahashi Rumiko Gekijou Ningyo no Mori

Synopsis

Yuta's recollections of his past continue. Yuta and Rin took a fishing boat and captured a mermaid to save Rin's father. However, the Sakagami islanders followed them and after killing both the mermaid and Yuta, they took Rin to Sakagami. When Rin saw Isago there alive, she realized that Isago was immortal. Isago revealed that she has been pregnant for three years by her previous husband, whom the Sakagami islanders killed. She needed mermaid flesh so she could finally give birth. Meanwhile, Yuta revived and returned to save Rin. The chief and his men alternately fought Yuta and Rin while they ate the mermaid flesh. However, many were poisoned by the mermaid flesh and the survivors, including the chief, became Deformed Ones. Isago told the chief that she too was a mermaid and leaped off a cliff into the ocean. Yuta and Rin thought Isago did so in desperation, but Isago changed into her mermaid form and swam away, trailed by two smaller forms. On Toba, Rin's father recovers from his wound without eating mermaid flesh. Back in the present, Mana asks Yuta how far does the ocean go.

(Source: Wikipedia)