As Charlie was singing to the people of Cannibal Town to invite them to go to war against Heaven, Alastor and Rosie stayed behind, singing together.

Rosie: They're dancing along, they're singing her song!

Alastor: Surprised? Why I knew she could do it all along!

Rosie then suddenly stops and turns to look at you, realizing you're still here as well, but she freezes as she starts seeing colors, meaning that you're her soulmate. Meanwhile, Alastor was inviting you to sing with them.