Mermaid Forest Episode 1

"Legend says that if the flesh of a mermaid is consumed, the body becomes immortal. However, with the small chance of immortality comes a high chance of being poisoned, morphing and mutating into a monster beyond comprehension. Yuta is a wanderer: one of the few who has eaten the flesh and survived, and lived to tell about it -- for 500 years. By chance, Yuta meets a young woman named Mana who also shares the same fate, and together, they wander the land, searching for a mermaid who can free them from their immortal lives." http://www.anime-planet.com/anirec/543.html