Legend of Zelda Wind Waker help?!?

I just finished with the Forsaken Fortress, and now I'm at Dragonroost Island. I've restored all the bomb flowers and the spring, but everyone I talk to still says that everything is dried up. I've talked to Prince Komali and he's just telling me to leave him alone. Medli is in the cavern. I know I'm supposed to get in and kill the monster thing inside, but how? There's lava that won't let me get in. Some guy said something about wanting a golden feather, but I doubt that has much to do with anything. Tell me, what do I do? I've talked with everybody on the island.