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 5 Gratitude Crystals. Link may also find fifteen Gratitude crystals at night in the islands of Skyloft, Pumpkin Landing, and Beedle's Island, but he may only find one at a time. After Link's Goddess Sword is upgraded to the Goddess Whitesword, he may dowse for them after speaking to Batreaux.

Uses
There are a total of 80 Gratitude Crystals found throughout the game. Bringing them 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 Crystals are designed to resemble the Japanese candy Kompeitō. Kompeito are hardened sugar formed into star shapes and are well recognized in Japanese culture. This gives Gratitude Crystals a resemblence to the Star Fragment treasure item in Spirit Tracks as well as the Star Bits in the Mario series, both of which were also designed to resemble Kompeitō.
 * The Gratitude Crystals are a notable mixture of earlier concepts. While their purpose is very similar to the Skulltula Tokens and the Poe Souls, the method of collecting them is reminiscent of Force Gems in Spirit Tracks.