Sweetie Belle, Rarity's younger sister and co-founder of the CMC and their Cutie Mark Camp. Sweetie is an average-sized mare with a love and talent for singing, writing songs, and vocal coaching.
At the camp, she heads the music activities, which involve both singing and playing instruments. Occasionally she does vocal coaching as well, both in and outside the camp.
When not working as a camp counselor, Sweetie Belle either models her sister's new works or teaches chorus class at the Ponyville schoolhouse. While she does do singing performances from time to time, she's found that she loves teaching others about the performing arts more than she likes being on stage. Sweetie lived with Rarity and their mom and dad for several years, before Rarity started up her first boutique and moved out of the house. She still keeps in touch with her older sister, even after the move to Canterlot. The two of them often go see musicals together whenever they have the time.
Sweetie and Scootaloo started dating in their older teens and decided to get married a couple years later. Thanks to some magic, they have two twin foals: Fizzle Spark, a unicorn filly, and Lilac Storm, a pegasus colt. She, Scoots, Apple Bloom, and Spike often meet together to catch up and give their kids a play-date.