The world of The Legend of Zelda: Skyward Sword HD is filled with collectibles, from traditional Zelda staples like heart pieces to unique items like Goddess Cubes and Gratitude Crystals. The latter are particularly valuable; you'll typically receive them when you help out the various residents of Skylot, and you can trade them in for some helpful rewards, including bigger wallets.
One side quest to earn Gratitude Crystals revolves around Bertie and Luv, the potion brewers in Skyloft's Bazaar. Here's what you need to do to complete the quest and earn their Gratitude Crystals. Be sure to check out our Skyward Sword HD guide roundup for beginner's tips, heart piece locations, and more guides. You can also read our full Zelda: Skyward Sword HD review.
For details on the rest, be sure to read our Gratitude Crystal quest roundup, including walkthroughs for each one, locations for individual Gratitude Crystals, and the rewards you can get from exchanging them.