Sekku (Seasonal Festival Days) (節句)

"Sekku" (in Chinese characters, written as "節句") means seasonal turning point when a traditional annual event is held, peculiar to Japanese culture and customs. In Chinese characters, Sekku is also written as "節供." Combined with Japanese customs, the calendar introduced from China was changed into Sekku. In ancient times, Sekku was called "Sechinichi," and on the dates of Sechinichi, seasonal court banquets called "Sechi-e" were held. Arranged for Japanese life, many Sechinichi were handed down to later generations, and during the Edo period, the Tokugawa shogunate designated five of them as the public event days or national holidays, and this was the beginning of Sekku.

The Five Main Seasonal Festivals' Days

Jinjitsu (Human's day)
This falls on January 7, and the festival is called "the Seven Herb Festival."
Joshi (or Jomi) - a term which means the first Snake day of March by the lunar calendar
This falls on March 3, and this date is called "Girls' Day," or "Dolls Day."
Tango (a term which means May 5 by the lunar calendar)
This falls on May 5 (by the solar calendar), and the festival is called "the Iris Festival."
Shichiseki (or Tanabata) - a term which means the evening of July 7 by the lunar calendar
This falls on July 7 (by the solar calendar), and the festival is called "the Tanabata Festival" or "Star Festival," in which a bamboo is used.
Choyo (a term which means September 9 by the lunar calendar)
This falls on September 9 (by the solar calendar), and the festival is called "the Chrysanthemum Festival."

Other

An iris that blooms on May the sixth/A chrysanthemum that blooms on September the tenth
These two flowers have value until May 5 or September 9, but not the next day. By extension, the two phrases are used metaphorically when a thing becomes useless because a good chance was missed. For example, Chritmas cakes and decorations are sold at a loss after December 25, and this is seen above.

Joshi, Tango, and Tanabata are on the same day of the week. The other two are not.