Kanō Jigorō
It is traditionally broken and eaten in a Shinto ritual called "kagami biraki" (mirror opening) on the second Saturday or Sunday of January. This is an important ritual in Japanese martial arts dojos. It was first adopted into Japanese martial arts when Kanō Jigorō, the founder of judo, adopted it in 1884, and since then the practice has spread to aikido, karate and jujutsu dojos.