Place butter into a microwave-safe bowl, and microwave until butter is melted, about 1 minute. Pour melted butter into a small microwave-safe casserole dish and mix grits, pineapple, and Cheddar cheese into melted butter.
Microwave grits mixture on full power until mixture boils and grits are tender, about 4 minutes. Sprinkle top with sugar and cracker crumbs.
Bake in the preheated oven until crumbs are lightly toasted, 15 to 20 minutes.