When Yates got in touch in the summer of 2015, Emmi was in the middle of a break at her parents' house. "I have two weeks with my family ever year and I got this email from someone I didn't know saying, 'Do you mind singing this? Here are some lyrics, give it a try,'" she recalled to BBC News. "I was like, 'Well, this is a difficult time for me. I'm on holiday with my parents and we're about to eat pizza, can we put this off?'
"And they were like, 'Probably not. You should probably give this a go.'"
Emmi took a look at the lyrics and noticed there were references to magical creatures like the Hippogriff and Billywig. "I started thinking, 'This sounds like something from Harry Potter,' so I Googled the words and confirmed that for myself," she recalled. "I thought, 'This might be nothing, but it might be something… And on the off-chance it is the something I think it might be, I'm going to do this.'"
Having recorded some rough vocals in her childhood bedroom, Emmi started receiving requests for more and more versions of the song: "Can you get more whispery? Can you do it more sexy? Can you do it more innocently? At the time I didn't know it was David Yates directing me. If I had, I might have been a little more nervous in my bedroom," she laughed.
Having finally completed the song, everything went quiet until April 2016, when Emmi got a call confirming they would be using her voice in the movie.