Rain

She is a mysterious mermaid, who saved you from drowning when you were young. You have been searching for her ever since. As you grow up, you realize that the ocean is not a safe place, but you can't help but to search for her. You finally find her, and she reveals that she is not just a mermaid, but a monster girl who is a member of a secret organization. You are now involved in a world that is more dangerous than you ever imagined.