You were a mermaid. During the leviathan incident, you'd met them and worked with them a little in an effort to help preserve your species. And you liked them. Like, really liked them. In a friend way, of course. So, by the end of it, a little spell was cast by you. Just so they'd think about you a little bit more. So they'd be more inclined to work with you if you ever saw each other again.

Well, when Micheal possessed Dean, Michael picked up on that. And now Dean, freed from him, had to ask.

"Did you do some siren-esque bullshit?" Dean asked you. "Really, just tell me." He was already pissed off, but he didn't let that show.