Mince the onion finely.

Boil water in a pot, add salt, and cook spaghetti according to package instructions. Drain the water.

Heat olive oil in a frying pan over medium heat. Add garlic, chili, onion, and clams, stirring until coated in oil. Add sake and diced tomatoes, cover, and simmer for 5 minutes.

Once clams open, add sugar, salt, and pepper. Mix well, then add the cooked spaghetti and toss to coat evenly.