This is a small, heart-shaped island where a Great Fairy dwells. Use the bombs to enter the Fairy Fountain in the large conch shell.
Blue ChuChu
Defeat the Blue ChuChu near the eastern palm tree for a Blue Chu Jelly.
Treasure Chart #40 (via Sea Platforms)
Sail up to the trio of Sea Platforms in this sector and destroy all the cannons on the two Sea Platforms that have ladders. This makes two chests appear on the ladder-less Sea Platform in the middle. Climb either of the Sea Platform’s ladders and use the Deku Leaf to float to the middle platform. Open the two chests located there to receive Treasure Chart #40 and a minor reward.
Bomb Bag Upgrade (via Great Fairy #4)
Bomb the wooden gate to open a way into the large conch shell. Drop into the hole there to enter a Fairy Fountain and find a Great Fairy. The Great Fairy upgrades your bomb-carrying capacity and invites you to return any time to replenish your Life Gauge or bottle a few Fairies.
Piece of Heart #31 (via Treasure Chart #4)
Finding and opening Treasure Chart #4 (which can be purchased for 900 Rupees from Beedle’s Shop Ship near Rock Spire Isle [B3]) allows you to pull up a chest containing Piece of Heart #31 from the Great Sea near Southern Fairy Island.