Takahashi Rumiko Gekijou Ningyo no Mori

Yuta has wandered for centuries after eating mermaid flesh and becoming immortal. Rather than welcoming endless life, he searches for a way to become an ordinary human again, eventually finding a companion in Mana, who shares his condition.

Their journey leads through places scarred by the same promise of immortality. Desperate families, old grudges and monstrous transformations reveal what people will sacrifice for a life without an end, and how easily that hope becomes a curse.