Peel daikon and cut into cylinders about ½ inch thick. Slightly shave the edges of each daikon cylinder. Cut konnyaku into 2 halves and then cut each half diagonally into triangles.
Bring a large pot of water to boil. Add daikon, konnyaku, and potatoes for 2 minutes. Remove with a strainer.
Add assorted fish cakes from oden set to the boiling water. Drain and set aside.
Combine dashi stock, soy sauce, mirin, and salt in a casserole pot. Bring it to a boil. Add daikon, konnyaku, potatoes, and mushrooms. Reduce heat and allow it to simmer for 30 minutes, skimming when necessary.
In the meantime, scald Napa cabbage in boiling water for 1 to 2 minutes. Do the same for spinach, about 30 seconds. Drain and squeeze out as much water as possible from vegetables.
Place cabbage leaves on work surface. Divide spinach into 4 and fold into neat bundles. Place each bundle on each cabbage leaf. Roll up cabbage leaves.
Place 2 cabbage rolls side by side and poke 2 bamboo skewers into the two cabbage rolls. Repeat with the other two cabbage rolls.
Cut cabbage rolls into half between the two skewers. Trim off edges.
Now, add assorted fish cakes, kombu knots, and skewered cabbage rolls to the oden. Continue to simmer for another 10 minutes. Turn off heat.