In a 6- to 8-inch frying pan over high heat, frequently shake sesame seed until lightly toasted, about 4 minutes.
Add oil, onion, ginger, and garlic. Stir until onion is limp, 2 to 3 minutes. Add sake, soy, and sugar. Bring to a boil. Serve hot, reheated (on grill), or at room temperature. If making ahead, cover and chill up to 5 days.