This page offers a guide on grabbing the Shine Sprite in Episode 8 of Noki Bay. This area is accessed by looking into the sun near the Shine Gate once you’ve collected 20 Shines back in Delfino Plaza.
Collect the Red Coins
Upon entering Noki Bay once more, you’ll be given the diving helmet again and instructed to head to the top and speak to the elder once more. Use the nearby rope to make the climb easier and speak to the elder there, who proclaims that the Noki people have prepared a treasure as thanks for helping them out. Once you’re ready, leap into the waterfall once again to be whisked off to the sea floor.
You’ll notice a large fish constructed entirely of both Gold and Red coins is swimming about here. There’s no set method for collecting all of these coins, save for keeping an eye on your Life and collecting a Gold coin should it start getting low. At times, the Red Coin Fish will split apart, causing the coins to scatter but after a few seconds, it will reform. Collect all of the coins and then drop to the bottom to claim your Shine.