Cut the green onion lengthwise, remove the core, and slice thinly. Soak in water and drain to make shiraga-negi. Slice the ginger thinly.

Cut the yellowtail into thirds, sprinkle with salt, and let sit for 10 minutes. Pat dry.

Heat the seasoning ingredients in a pan until boiling. Add the yellowtail, ginger, and green onion core. Simmer over medium heat while spooning the sauce over the fish until its color changes.

Cover with a drop lid and simmer on low heat for 10 minutes.

Remove the drop lid and simmer over medium heat until the sauce thickens. Spoon the sauce over the fish occasionally.