Sylphy is a minor antagonist-turned-ally in Kilala Princess. She's the princess of Floradiso, and Rei's fiancée. Despite it being an arranged engagement, Sylphy is in love with Rei and is thus Kilala's rival.
Sylphy suddenly appears at the beginning of the chapter in Beauty and the Beast 's universe. She presents herself as Rei's fiancée (he never mentioned her before but doesn't deny it), and also as a princess, but despite of this Sylphy shows a serious lack of manners and is very self-centered. Kilala once told her that in spite of her beauty and title, Sylphy lacks a heart able to empathize. She was conceived as Kilala's opposite, and wear skimpy outfits for that reason, though they seems out of place for a princess. She don't have powers of her own (only a talent for music) but her necklace is a spying device for Valdou.
Sylphy justified her first apparition with her concerning for Rei, but was actually sent by Valdou, who promised her she could marry Rei if she brought him back to Paradiso. Kilala escaped from prison, then went to stop Sylphy. Valdou lied, and was certainly going to brainwash Sylphy. The latter was finally convinced, reformed and helped Rei and Kilala to escape to Aladdin's world.
Back in Paradiso, she takes part in the battle against Valdou and his humanoids and finally witnesses Rei's asking for Kilala's hand. But Sylphy accepts this, and is lastly seen attending their wedding. It's mentioned afterwards Sylphy gave Paradiso Kingdom free building materials to help it repair its fire damages.