There are so many things that you can put in Miso soup. Miso soup’s golden couples are;

Patato & Onion, Mushroom & Leek, Kumara & Onion, Mungbean & Tofu, Cockle & Spring onion, Daikon Radish & Wakame seaweed, Spinach & Egg, Egg plant & Mizuna, Turnips & Turnip’s leaf, Cabbage & Potato, etc….

My favorite is Potato & Onion. Sweetness from potato & onion makes Miso soup much more flavorful.

Basically there are no rules. You could use pretty much anything that you want to eat with Miso soup. Also you could put more than two ingredients.

And some unusual couples are;

Bacon & Tomato, Crayfish Head & spring onion, Natto & Egg….