Mermaid Forest

Five hundred years ago, Yuta ate mermaid flesh without knowing what it was, and now he can't die. That sounds like a gift until you spend a few centuries watching everyone around you age and disappear while you stay exactly the same. He's been wandering Japan ever since, searching for a mermaid who might be able to undo what was done to him. When he finally finds one, things get considerably darker — turns out mermaids have their own agenda, and it involves keeping a young girl named Mana as a long-term food source. Yuta steps in, and now the two of them are traveling together, both carrying a curse neither asked for. The show is only 11 episodes, so it stays tight and focused — each arc drops them into a new situation involving immortality, mermaids, and the kind of people willing to do ugly things to live forever. The tone is consistently dark and a little unsettling, which is a genuine shift if you only know Rumiko Takahashi from Inuyasha or Ranma. This is much closer to Petshop of Horrors or Mononoke in mood — quiet dread over action, moral ambiguity over clear heroes. The mermaid mythology here is genuinely strange and nothing like the Western version. If you want a short, atmospheric horror-fantasy with two quietly compelling leads and a concept that keeps finding new ways to ask what immortality actually costs, this one delivers.