Japanese winters are very sunny and dry in Tokyo area. If there is not too much wind day time sun is fairly warm, but as soon as it gets dark the temperature drops and it becomes freezing cold. A hot veggie soup is perfect to warm and rehydrate at the same time.
My classic is a base with 1 leek, 2 big carrots, 2 small potatoes. I diced them and cook them in water with 1 leaf of laurel and a bit of olive oil, salt and pepper.
Then if I want something a little bit more nourishing I add this marvelous Italian mix of lentils, beans and barley that I buy at one of the NYC Eataly shops in Tokyo.