Showa Day is the 1st of 4 public holidays held during Golden Week falling on April 29 to honour the birthday of the Showa Emperor, who reigned from 1926 to 1989.
While the birthday of each Emperor (Tenno Tanjoubi) has always been celebrated in Japan, when the Emperor’s reign ends, the date changes and ceases to be a holiday.
In the case of the Showa Emperor, since his birthday fell during the Golden Week national holiday period, the government decided to continue to keep April 29 as a public holiday even after his death in 1989 as they felt taking away this public holiday would have a negative impact on the citizens. They did however, change the name of the holiday to Midori no hi (Greenery Day) since there was a new emporer and a new date in December celebrated as Tenno Tanjoubi. It’s thought the name Greenery Day was chosen because the Showa Emperor had a great love of nature. Then in 2007, the government decided to move Greenery Day to May 4 and rename the April 29 public holiday as Showa Day.
While many public holidays in Japan have rituals or customs attached, Showa Day, has no customs as such although it’s supposed to be a day when people reflect on the Showa Period. How people choose to do that is a very individual thing and somewhat controversial considering that WWII took place during this period.