The Legend of Zelda: Skyward Sword/Gratitude Crystals

The Gratitude Crystal Sidequest can be started as soon as you bring the Ruby Tablet back to the Goddess Statue on Skyloft. When Kukiel goes missing you find her in the company of her friend, the demon Batreaux (see mission below for details). Batreaux however is not evil, and in fact wants to get rid of his demon guise. He hopes to accomplish this by collecting Gratitude Crystals. These conveniently appear when you help people. Of course Batreaux can't just wander around Skyloft, so he deputizes Link to collect the Crystals for him, offering rewards at certain intervals.

This guide will help you find all the Gratitude Crystals in the game. Most can be collected by helping out the various inhabitants of Skyloft in self contained missions, but 15 Crystals can be found just lying around the place at night.

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 can obtain 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 Batreaux 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.

Skyloft by Night
As mentioned above, 15 Gratitude Crystals can be found just lying around during the night. 10 of these are accessible right away. Here are the locations of these 10 Crystals. Sleep in any room to make it nighttime before starting Now go back to the academy and sleep until morning. You can now go to Batreaux and claim the first 2 rewards.
 * If you sleep in Link's room, you can grab the first crystal right there
 * Leave the academy on the ground floor and walk over to the Sparring Hall. he crystal is hidden in the rafters in the back of the room. Use the beetle to grab it.
 * One Crystal is inside the Academy right next to the front door on the upper level.
 * If you leave the academy grounds by the gate on the lower floor, the first house on the left you will encounter is Parrow and Orielle's. There is a crystal in the corner of there living room.
 * Right across from this house is the southern Windmill and to its right you can climb down some vines to a platform that has a crystal (if you are lazy, the beetle can fly down there and grab the crystal)
 * Moving further south, you reach the main Plaza with the Light Tower. Climb to the base of the tower and walk around it to find a crystal
 * Go east and across the bridge to the residential area. Find the big pumpkin patch. There is a crystal behind the tree in that area
 * Now use the stones to jump across the river to the Waterfall cave. Fight your way through the cave and a Crystal awaits you at the exit.
 * Move on toward the small cave where you found Link's Loftwing earlier for another Crystal
 * When you run back to the academy to rest, stop at the norther exit of the Bazaar. One level down (going east) are wooden planks and on the next grassy patch is the last Crystal (This one is hard to explain. It can help to use the beetle to scout the area and grab the Crystal)

Rescuing Orielle
This mission can be undertaken as soon as Kukiel has returned home, but there is no hurry, because you can't get enough Gratitude Crystals for the next reward until later anyway.

When you cross the main Plaza next to the Lighthouse, you see Parrow stalking around with a bubble over his head (the international signal for 'I have something to say'). It turns out that Orielle has taken her Loftwing out for a ride, and has not returned. Of course, it's up to you to find her (what exactly are all those knights doing all day). The hint here is that she had wanted to check out the 'colorful island' in the west (you might not have visited this island yet, unless you did some exploring). Get airborne and fly West (use a beacon on the island and head straight toward it). Stay relatively low, or you might miss the very small island where Orielle made an emergency landing. Her Loftwing is hurt and could Link please get some medicine from Parrow?

Go back to Skyloft and make sure you carry and empty bottle (one would think Parrow could spare one right?). Talk to Parrow and he will give you Loftwing medicine (Mushroom Spores). Head back out west and witness the workings of this miracle drug that heals broken wings in seconds. 5 Gratitude Crystals will appear from Rescuing Orielle. To double your reward head back to Skyloft and give Parrow the happy news for 5 more Crystals will appear. That brings your total up to 25.