Cut the daikon into 2cm thick slices, peel the skin, and halve them. Place on a microwave-safe plate, add 1 tbsp water, cover loosely with plastic wrap, and microwave at 600W for 5 minutes. Drain the water. Remove the seed from the umeboshi and roughly chop it.

Sprinkle salt on the yellowtail fillets and let sit for 5 minutes. Pat dry with a paper towel and cut into bite-sized pieces.

In a pot, combine the seasonings (sake, mirin, mentsuyu, and water) and heat over medium heat. Once boiling, add the daikon, umeboshi, and ginger. Cover and simmer on low heat for 10 minutes.

Remove the yellowtail and daikon from the pot and place them on a serving plate.