The Legend of Zelda: Skyward Sword/Gratitude Crystals

The Majority of the Gratitude Crystals are gathered doing quests given by numerous characters.

Rewards

 * 5- Medium Wallet
 * 10- Piece of Heart
 * 30- Big Wallet, and Cursed Medal
 * 40- Gold Rupee
 * 50- Giant Wallet
 * 70- Gold Rupeex2
 * 80- Tycoon Wallet

Wryna's Request
You get this request automatically after placing the Ruby Tablet fragment into the Ancient Tablet's aperture in the Statue of the Goddess. Wryna's daughter, Kukiel, has gone missing and she fears a monster is somehow involved. Talk to Parrow in the plazza and his sister, Orielle, to recieve the most useful clues: that there is a monster rumored to live in the graveyard, and an old man who spends most of his time hanging out at the Lumpy Pumpkin claims to have seen it. Fly out there and speak to him. The old man tells you that if you go to the graveyard at night and hit the headstone closest to the tree, the door to the storehouse will mysteriously open. You also need to push the headstone after you hit it with your sword. This opens the door to the storehouse. When the storehouse in the graveyard opens, walk to the ladder and climb down. This takes you to an isolated house that sits on a series of isolated platforms beneath Skyloft. You'll find Kukiel inside the house with her "friend," who turns out to be a horrible-looking monster whose name is Batreaux. Despite Batreaux's terrifying visage, he's actually a kind-hearted soul who loves people. Unfortunately, he scares the snot out of most townspeople, so he can't live above in Skyloft with everyone else. Batreaux has heard that if a monster caobtain enough Gratitude crystals from humans, though, that monster will transform into a human. Naturally, Batreaux wants Link to go out and gather all the Gratitude Crystals for him. This may sound like Batreaux game the system, it's ultimately for the best that you do this for the poor guy. Begin after you meet Batruex by sleeping until, then going to Kukiel's house and speaking to Wryna inside. Kukiel has returned home, as promised. Her mother gives you your first stack of 5 Gratitude Crystals.

Knight Academy

 * A Gratitude Crystal is in Link's own room at night.
 * By sneaking into Zelda's room through the chimney, Link will find another Gratitude Crystal in her wardrobe (Requires the Clawshots).
 * A third is found on the rightside plant by the top exit.