didn't the raccoon lady just say he wasn't immortal & that mermaid boy knows the "cure" for his non-immortal immortality? ...this was a confusing update... （￣-￣）
Maybe it’s because he’s eaten part of a mermaid, his life is lengthened and he heals faster, but that is not immortality. Eventually it will wear off and he will die. He’s even aging, because he only eats a little bit of it too. His mer-husband looks like a child when he turned into a human, and looks significantly younger when he’s in his normal form, despite being way older. He is immortal, not the human. Kiyo just lives for a long time and heals from serious injuries quickly, that it feels immortal. ?? That’s my best guess.
I think Kiyo is not immortal. Maybe he's like the homunculus in fma where he has a few lives