Score the skin of the sea bream fillets with a cross-cut. Cut the green onion into halves lengthwise, remove the core, and slice into thin strips. Soak the strips in water for 10 minutes, then drain (to make shiraga-negi). Slice the ginger thinly.

In a pot, combine the braising sauce ingredients and heat over medium heat until boiling. Add the sea bream fillets and ginger, cover with a drop lid and a regular lid, then simmer over low heat for 10–15 minutes.