Separate an egg into yolk and white. Cook the soba noodles and soak in cold water. Stir the natto well until it foams.
Beat the egg white until stiff peaks form. Mix in the natto very well with chopsticks, until you can see sticky threads. You can add the natto sauce, too.
Serve the soba noodles in a noodle bowl. Pour on the egg white and natto mixture from Step 2 and place an egg yolk in the centre. Sprinkle the seasoning and pour Japanese noodle dipping sauce on it. I used 1 pack of natto for mixing with the egg white, the other for the topping.