Clean the sea bass by removing scales, gills, and guts. Rinse and pat dry with kitchen paper. Make slits on the fish and season with salt and sake for preparation.

Slice the ginger thinly with the skin on. Cut the green onion lengthwise, remove the core, and slice into thin strips. Soak the strips in water, rub gently, and drain to make shiraga-negi (thinly sliced green onion).

Place kombu, ginger, green onion core, sake, and water in a frying pan. Heat over medium heat until boiling, then arrange the sea bass in the pan. Cover and steam for about 7 minutes until cooked through.