Kagami biraki: The opening of New Year's rice cakes
Kagami biraki is the practice of eating the kagamimochi (round mirror-shaped rice cakes) that were offered to the gods. It is supposed to bring a sense of closure to Osyogatsu (New Year’s Holidays). Kagami biraki is to get power from the year gods to live happily for one year. For Kagami biraki, people use a wooden hammer or hands to cut the Kagamimochi into smaller eatable pieces instead of regular knives.
By the way, the word “Kakimochi (sliced and dried rice cakes)” comes from “kaku” (cutting the Kagamimochi into smaller pieces).