Cook the spaghetti according to package instructions and drain.

Cut the boiled octopus into bite-sized pieces and trim the asparagus into small sections.

Sauté the shimeji mushrooms and asparagus in a pan with butter until tender.

Mix the natto with its sauce and combine with the sautéed vegetables and octopus.

Add the cooked spaghetti to the pan and toss with the salted kombu and mentsuyu.