Emperor Jimmu
The origin of National Foundation Day is New Year's Day in the traditional lunisolar calendar. On that day, the foundation of Japan by the mythical Emperor Jimmu was celebrated based on the "Nihon Shoki", which states that Emperor Jimmu ascended to the throne on the first day of the first month. There is, however, no historical evidence that Jimmu actually existed, and the year 660 BC is far earlier than any known emperor. It is considered to have been arbitrarily chosen based on an ancient Chinese belief that that year would have been an auspicious one for revolutionary change.