Cadenza Crystal is a siren who can sing without a pendant. She is one of the rarest species of sirens in Equestria, where Princess Twilight Sparkle lives. The main thing about her is that she doesn't want to become evil. Sonata Dusk tries to hide her feelings from Adagio Dazzle and Aria Blaze to keep it a secret to herself. Cadenza soon figures out Sonata's problem and asks her to talk to her about it. As Sonata told her about her hidden feelings for her, Cadenza then understands that Sonata feels sorry about her evil actions. For the first time in her life, Sonata decides to become a different siren, with Cadenza's guidance.

Note: This happened after the Battle of the Bands in Rainbow Rocks.