Miya is thinking ahead here, anticipating the holidays and especially the Japanese tradition of serving ozoni, or mochi rice soup,  on the first day of the new year.  Sometimes things are created by accident-----she used carrot tops for greens because she didn't have the traditional mizuna nor mitsuba, nor shungiku.  It had a certain bitterness just like the mitsuba and was wonderful in the soup.  I thought maybe arugula would be good as well.  So, a traditional Japanese soup gets a different twist because if you dont have the ingredients, you use what you have, and sometimes you come up with a new winner----not Japanese in its entirety -----a different soup, but still Japanese in spirit---but that's the spirit of Amasia, to update something that's been around for a long time.