Gratitude Crystal

A Gratitude Crystal is an item featured in Skyward Sword. Link can obtain these crystals by doing good deeds to the various people he meets throughout his adventure. Upon doing so, the person that was helped will be overwhelmed with feelings of thankfulness, emitting enough energy to create the Gratitude Crystal.

Uses
Bringing the Gratitude Crystals to Batreaux, who wants to use these items to become human, yield various rewards to the young hero, including upgrades for his wallet, satchels, and his Adventure Pouch.

Trivia

 * The Gratitude Crystal resembles the Star Fragment treasure item in Spirit Tracks as well as the Star Bits in the Mario series, the latter of which drawing inspiration from Kompeitō.