During the course of the game, you’ll be able to find these special items called Gratitude Crystals. Much like the Skulltula Tokens of Ocarina of Time, you collect them a while until you gain a reward; however, the rewards will come much faster here. To find them, you generally finish these side-quests for people around Skyloft, although you find 15 Gratitude Crystals that are … just there.
You’ll be able to start this upon unlocking the Eldin Volcano area. After that initial side-quest, you are generally able to go around and complete the rest, except there are certain things you’ll need for most of them.
Anyhow, during the first side-quest, you learn of Batreaux, the one you are to give your Gratitude Crystals to for rewards, which are as follows:
- 5 Gratitude Crystals: Medium Wallet (base capacity of 500 Rupees).
- 10 Gratitude Crystals: Piece of Heart.
- 30 Gratitude Crystals: Big Wallet (base capacity of 1,000 Rupees) and the Cursed Medal.
- 40 Gratitude Crystals: 300 Rupees (one Gold Rupee).
- 50 Gratitude Crystals: Giant Wallet (base capacity of 5,000 Rupees).
- 70 Gratitude Crystals: 600 Rupees (two Gold Rupees).
- 80 Gratitude Crystals: Tycoon Wallet (base capacity of 9,000 Rupees).