Cut the yellowtail into thirds and pour boiling water over it to remove odor. Drain and pat dry.

Peel the lotus root and cut it into quarters lengthwise. Slice into 7–8mm thick pieces and soak in water to remove bitterness. Drain. Slice half of the ginger thinly with skin on, and julienne the rest after peeling. Soak the julienned ginger in water and drain.

In a pot, combine water, sake, mirin, sugar, soy sauce, and the sliced ginger. Bring to a boil. Add the lotus root and yellowtail, cover, and simmer over medium heat for 7–8 minutes.