"Zouni" is one of the Japanese traditional food eating in the new year. It is the soup containing rice cake and vegetables. But there are so many recipes of zouni. It depends on the region. My zouni is made from dashi (Japanese soup broth), soy sauce, sake, mirin and brown sugar. The other ingredients are chicken thigh, daikon radish, carrot, shimeji, and rice cake.
Rice cake had been precious food for ancient people. They used to give rice cakes for Toshigamisama. (the god who comes to each home in the new year) Then people used to eat the offering as zouni.
When Japanese eat zouni, they thanks for the wellness of last year and pray for the well-being for their family again.