For noodles:: Bring a large pot of water to a boil. Put the noodles in the boiling water and lower the heat. The water should just bubble gently, not be at a rolling boil. Stir gently. Cook for 5 to 8 minutes until noodles are cooked through, a bit past the al dente stage.
Drain the noodles and rinse under cold water to cool quickly. Rinse until noodles are smooth and firm and not at all sticky. Allow noodle to drain in colander while the rest is being prepped.
For dipping sauce: combine dashi and kaeshi. Pack in a leak-proof container.
For crab salad: Massage the cabbage with the salt until the cabbage has wilted. Squeeze well to expel excess moisture. Put in a bowl, add the vinegar and sugar, and mix. Add the crab and taste; add a little more salt if needed. Sprinkle with sansho or black pepper.
To pack: Put the noodles in one compartment, sprinkle with green onion, keep nori and sesame seeds separate. Pack crab and cabbage salad in a divider cup. Halve egg and pack near noodles. Fill in any gaps with cherry tomatoes.