In an 8- to 10-inch frying pan over medium heat, stir garlic and onion in olive oil until golden brown, about 2 minutes.
Add shrimp and sake. Stir often until shrimp are opaque but still moist-looking in center of thickest part (cut to test), 2 to 3 minutes.
Add butter, soy sauce, and parsley; stir until butter is melted and blended into sauce.
Spoon into 4 small shallow bowls. Serve with crusty bread or hot cooked rice.