Romi is known for being one of the most famous pop singers at the time, along with her sister Montana. Together they have merchandise called Twin Hearts that they sell in many stores. In If You're Reading, This It's too Late, they decide to sell an item called Sock Roaches, which look exactly like the Homunculus that Cass had sewn. Amber is the first one to wear them, and lets Cass, Max-Ernest and Yo-Yoji have a "sneak peak."
In book two, it is proven that the Skelton Sisters cannot sing and actually just lip sync in one of their concerts. Cass, Max-Ernest and Yo-Yoji stood up on stage with them and yelled negative things about them into the microphone, such as "the Skelton Sisters suck!". While they did have fun doing that, it was also to distract the crowd from what they were really doing: trying to help save the Homunculus.
Romi is apart of the Midnight Sun, along with Montana. Ms. Mauvais was using them in the second book to sing the tune of the Homunculus's song, but make it look like it was just some ordinary song that they wrote. They do this again in the fifth book.