Goddess Plumes are Treasures used to UpgradeItems at the Scrap Shop. They rarely appear in place of Dusk Relics or Amber Relics, with a slightly higher likelihood of this happening in Dungeons. Additionally, they're available as a random reward from all minigames once the primary reward has been obtained, and are available in numerous chests around Hyrule and the Sky. Keese may drop them in extremely rare circumstances.
Goddess Plumes are required for the following upgrades:
↑"Goddess Plume A wondrous stone said to have been dropped by the goddess herself. Finding one of these items is an extremely rare occurrence." — Collection (Skyward Sword HD)
↑"获得了女神的遗失物!" — N/A (Skyward Sword HD, Simplified Chinese localization)