Gratitude Crystal

Gratitude Crystals are items from The Legend of Zelda: Skyward Sword. These crystals are physical manifestations of peoples' feelings of gratitude, and may be found scattered throughout Skyloft, the Lumpy Pumpkin, and Beedle's island at night. Gratitude Crystals may also be gained after completing various side-quests for people. Gratitude Crystals may be exchanged with Batreaux for several rewards, as collecting all 80 of them will transform him into a human. Humorously, Kukiel refers to them as "grabitude crackles."

Rewards

 * 5 Crystals: Medium Wallet
 * 10 Crystals: Piece of Heart
 * 30 Crystals: Big Wallet, Cursed Medal
 * 40 Crystals: 300 Rupees
 * 50 Crystals: Giant Wallet
 * 70 Crystals: 600 Rupees
 * 80 Crystals: Tycoon Wallet

Origin
Gratitude Crystals resemble Star Bits from Super Mario Galaxy and Super Mario Galaxy 2. As characters from the Mario series have had cameo appearances in several past installments of the Legend of Zelda series, it is possible this was an intentional design choice.