The Kingdom of Mewni. Butterfly Castle.

Selena Butterfly, the youngest daughter of Moon and River and the sister of Star. In Selena's room, she is thirteen years old. She has blue circles on her cheeks.

Older sister, the Star Butterfly, was given more attention than Selena.

Selena and Star sleep in separate rooms. Star's is more vivid and colorful room, various color posters and girly stuff. Selena's is more gloomy, with bookcases filled with books in her room. Selena can use magic, but none of her parents or Star's sister knows this, except Glossaryck.

Selena already used to that they don't notice her and doesn't seek their attention or care. Because it's already useless.

And while Star is taking lessons with the family artifact with Glossaryck, meanwhile, Selena was sitting in the library reading a book.