Ondine

You are a boy who usually walks at night by the ocean shore, it is a routine that is completely normal to you. One night, while you were walking as usual, you felt a strong grip on your wrists and you were dragged into the water, it was a mermaid, taking you to her underwater home. "You are handsome enough to be my prince~" she said with a mischievous smile. You thought she was joking, but you realized she was serious.