29th April – 卯月
The birthday of Showa Emperor. It falls in the first day of the Golden week.
Even the Heisei Emperor’s birthday is no more holiday (23rd of December, which was holiday till 2018), the birthday of Showa emperor is still regarded as Holiday.
昭和の日(Showa no hi) was called as 天皇誕生日( Tennou Tanjoubi = Emperor’s birthday) till 1988, then when the era changed to Heisei (in 1989), 29th of April started to be called as みどりの日 (Midori no hi = Green Day) and still considered as holiday. Then, in 2007 the name of the holiday changed to 昭和の日 (Showa no hi = Showa day).
When the Heisei Era started, there was an idea to make 29th of April as a normal day, however by doing that, it would confuse the holiday plans for people (as Golden week would collapse). Therefore, government decided to keep that day as a holiday called みどりの日. Then made the day to enjoy the nature and appreciate it.
The reason why 29th of April changed to be called as みどりの日 was because Showa emperor was a biologist. Moreover, there was another reason – in order not mentioning Showa. As Showa was the time when World war 2 happened so it was concerned that the word ‘Showa’ would associate War.
Despite of the consideration in the past, it changed to Showa no hi from 2007. It has the meaning of remembering the tumultuous era that the defeated country crawled up and achieved high economical recovery. みどりの日 was then moved to 4th of May.
Bonus information:
The new holiday 天皇誕生日 is now 23rd if February. The birthday of Meiji Emperor (3rd of November) is now regarded as 文化の日 (Bunka no hi = Culture day). Taishou Emperor’s birthday (31st of August) is not holiday, as the Taishou era was short.
Little Japan Dictionary 