The Serenade to Kaysa in The Legend of Zelda: Tears of the Kingdom can be started by speaking with Mastro at the Outskirt Stable. For this quest, you’ll need to find Pyper, the flautist. Make your way south to Highland Stable in Faron.
Once there, head to the north side of the stable and look for Pyper in a tree near the building supplies pile.
Climb up the tree then speak with him to receive The Flute Playter’s Plan. Before Pyper is willing to return to the Stable Trotters, he’ll need 10 sunset fireflies. These fireflies can be collected at night by sneaking up to fireflies! Once you have enough, hand them over to Pyper. He’ll need you to bring Haite to the tree at night. To change the time, either wait or rest at the stable. Once it’s night, speak with Haite in the stable then guide her to the tree. As you approach, Haite’s wish will come true. As a reward for helping him out, Pyper will give you a Big Hearty Truffle and The Flute Player’s Plan will complete.
Now that Pyper has returned to the Stable Trotters, head back to Outskirt Stable and speak with Mastro. The breezer of course will need help getting up the hill so you’ll need to construct a contraption to get the job done! When you’re ready, speak with Mastro to get the crew to hop in. Drive them up the hill to play for the Great Fairy! After the performance, you’ll receive a silver rupee and the Serenade to Kaysa side adventure will complete.