Greenery Day Wikipedia
The present observation of Greenery Day (みどりの日, Midori no Hi) as a national holiday in Japan stems from the celebration of the Emperor Shōwa's birthday on April 29 every year during the Shōwa era. In 1989, following the ascension of the current Emperor Akihito to the Chrysanthemum Throne, the name of the holiday was changed from "Birthday of the Emperor" to "Greenery Day". Officially, as its name suggests, it is a day to commune with nature and to be thankful for blessings. The day was renamed to "Greenery Day" to acknowledge the controversial wartime emperor's love for plants without directly mentioning his name. However, in practice it is seen as just another day that expands the Japanese Golden Week vacation.
In 2007, Greenery Day moved to May 4, and April 29 was changed to Shōwa Day in accordance with a 2005 revision of the law pertaining to public holidays. The Shōwa Emperor reigned for 62 years and 2 weeks. On May 3, 1947, he became a symbol of Japan by the new constitution of the country.