Infinity Nikki features many legendary creatures, some quest-related, others hidden. Examples include the Dawn Fox, Tulletail, Bullquet, and the Astral Swan. While you can groom the Astral Swan and obtain its Astral Feather independently of a quest, the Soaring Above the Starry Sky quest provides helpful context.
Soaring Above the Starry Sky Quest
To begin, locate the Stellar Fishing Ground Peak Warp Spire and speak with Curious Pinny. The quest involves visiting Lensie's house (easily found using the map's tracking system), grooming the Astral Swan, equipping the Floral Gliding outfit, and flying with the swan. After the flight, return to Pinny and Lensie, then visit Elron in Stoneville to complete the quest.
Grooming the Astral Swan
Grooming is simple: use the Bye-Bye Dust or a similar grooming Ability Outfit. This will also reward you with an Astral Feather.
Equipping the Floral Gliding Outfit
Equip the Floral Gliding Ability Outfit to fly with the Astral Swan. It's recommended to change into the full outfit set from your wardrobe.
Flying with the Astral Swan
Activate the Floral Gliding outfit near the Astral Swan to initiate a cutscene. During the flight, stay close to the swan and avoid drifting. Press the "Soar" button when prompted. Crucially, don't deactivate the Floral Gliding outfit until the Astral Swan has fully landed. Prematurely ending the flight will prevent mission progression.