Kagami Biraki is a traditional Japanese ceremony that occurs at the beginning of the new year. The fourth Tokugawa Shogun, Tokugawa Ietsuna, was the first one to hold Kagami Biraki 300 years ago. Before going to war he gathered his daimyo in his castle to break open a sake cask. The battle was successful, so from there the ceromony was born.
In the martial art Aikido Kagami Biraki usually signifies the first practice of the year.
The term Kagami Biraki literally translates to “Opening the Mirror” or “Breaking of the Mochi”. Mochi being a rice cake made of glutinous rice pounded into paste and molded into shape.