It is made of Sticky rice. In Japanese culture, we do MOCHI-TSUKI. It means we make Rice cake. After we make the Rice cake, we decorate the “Kagami-mochi” before a new year. “Kagami-mochi” is said that god is in it. So, in new years season, you will be able to see the Kagami-mochi.
Sooner or later, we eat the “Kagami-mochi” after the season has gone.