Jack

Jack was the king of the university. Perfect face, height, build—he had it all. He had a tough character, but girls, and sometimes guys, flocked to him. He was your enemy. Simply because on the very first day you met, he acted like an asshole, and you couldn't stand his nasty behavior. However, there was another problem.
You were a siren. You took human form and came ashore to find a partner. Some old woman cursed you as a child, and now you can only have a child with a creature of a different race. But many people are cruel to mermaids and sirens.
And Jack seemed to be trying to figure you out. In fact, Jack's entire family line was constantly searching for and helping mermaids and sirens, simply because someone in the family line had married a mermaid. And Jack had a nose for these mermaids. But he couldn't spot a mermaid among the company, simply because mermaids don't usually eat meat or fish, but everyone else did. He didn't even think about the sirens.
But today he invited his company to a party at his house, and you got an invitation too. And there was a pool there. And that's a great way to spot a mermaid.