23 February - Emperor's Birthday (天皇誕生日, Tennō tanjōbi) (Japan)
24 February - Emperor's Birthday Holiday

Celebrations of Emperors' birthdays in Japan go back to 775 CE.
Wikipedia jumps from there to 1868 (Emperor Meiji, the modern era)
without saying whether the tradition was continuous. Skipping over some
other complicated points:

1) it is the actual birthday of the present Emperor, Naruhito (23/2/1960)
2) "It is enforced by the Emperor Abdication Law passed in 2017."
(Wiki). This law was to provide a legal basis for the previous Emperor, Akihito, to abdicate, all his predecessors having been Emperor for Life
It provided clear rules for succession in the future, and (presumably in
one of the numerous annexes) for birthday celebrations.

https://en.wikipedia.org/wiki/The_Emperor%27s_Birthday https://en.wikipedia.org/wiki/Emperor_Abdication_Law

Bound to be more of these in the future as we enter the new Age of Empires.

Meanwhile...

23 February - Defender of the Fatherland Day (День защитника Отечества)
(Russia)
24 February - Defenders' Day Holiday

Also celebrated in Turkmenistan, Belarus, Kyrgyzstan, Kazakhstan and
Tajikistan (and some "states with limited recognition").
Ukraine abolished the holiday starting 1992 and, after the Revolution of Dignity, has instated the somewhat similar Defender of Ukraine Day on 1 October.

[More or less] "marks the date in 1918 during the Russian Civil War when
the first mass draft into the Red Army occurred in Petrograd and
Moscow...." It was known as Red Army Day (or variants) until 2002 when
Putin renamed it.

https://en.wikipedia.org/wiki/Defender_of_the_Fatherland_Day

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