https://en.wikipedia.org/wiki/Japanese_era_name"The system on which the Japanese era names are based originated in China in 140 BCE, and was adopted by Japan in 645 CE, during the reign of
Emperor Kōtoku.
The first era name to be assigned was "Taika" (大化), celebrating the political and organizational changes which were to flow from the great
Taika reform (大化の改新) of 645. Although the regular practice of proclaiming successive era names was interrupted in the late seventh century, it was permanently re-adopted in 701 during the reign of Emperor Monmu (697–707). Since then, era names have been used continuously up through the present day.
[1]"
Mutsuhito assumed the throne in 1867, during the third year of the
Keiō (慶応) era. On 23 October 1868, the era name was changed to "
Meiji" (明治), and a "one reign, one era name" (一世一元,
issei-ichigen) system was adopted, wherein era names would change only upon immediate imperial succession. This system is similar to the now-defunct Chinese system used since the days of the
Ming Dynasty. The Japanese nengō system differs from Chinese practice, in that in the Chinese system the era name was not updated until the year following the emperor's death.
In modern practice, the first year of a nengō (元年,
gannen) starts immediately upon the emperor's accession and ends on 31 December. Subsequent years follow the
Gregorian calendar.
For example, the Meiji Era lasted until 30 July 1912, when the Emperor died and the
Taishō (大正) era was proclaimed. 1912 is therefore known as both "Meiji 45" and "Taishō 1" (大正元年,
Taishō gannen), although Meiji technically ended on 30 July with Mutsuhito's death. "
And now starts a new era with the new emperor
https://www.japantimes.co.jp/news/2019/03/31/national/japan-keep-official-records-new-era-names-selection-process/#.XKEw1MKP4dV Emperor Akihito is accompanied by Empress Michiko and Imperial family members (from left) Princess Yoko, Princess Akiko, Princess Nobuko, Prince Akishino and Crown Prince Naruhito, as they arrive at the autumn garden party in Tokyo in November 2014. | APKind regards, Paul.