Place kombu and water in a pot and let sit for 30 minutes.

Prepare vegetables: cut pumpkin into bite-sized pieces, slice daikon and carrot thinly, cut leek diagonally into 1cm slices, slice shiitake mushrooms, and separate shimeji mushrooms.

Cut pork belly into bite-sized pieces.

Heat the pot with kombu and water over medium heat until just before boiling, then remove kombu. Add bonito flakes and simmer for 2 minutes, then strain the broth.

Bring the broth to a boil, add pork belly, and skim off any foam. Add daikon, carrot, leek, shiitake, and shimeji mushrooms. Cover and simmer on low heat for 4–5 minutes until vegetables are tender.