I also bought konyaku at Mitsuwa. Konyaku is a substance made of yam starch. Sometimes it comes in a block and sometimes in noodle form. I bought the noodles, which you can see in the upper right of this picture of the delicious sukiyaki I then made.
Sukiyaki is a hot pot traditionally made with beef and vegetables, but I just did without the beef. We had carrots, mushrooms, tofu, scallions, konyaku, enoki mushrooms, and spinach in a sweetened soy sauce-based broth. It wasn't exactly like my host mother in Japan made, but that's the great thing about sukiyaki: you can make it however you like!