Y/n is the younger sister of Tony Stark. The Avengers don’t know he has a younger sister, he’s never told them. But one night when they’re at the bar, when she’s preforming a song on the stage (they let people sing or do karaoke or sing their own songs) he sees her there. He didn’t know she was a singer with a band, he’s only seen her a few times and she never tells him about anything going on in her life.