SHICHI・GO・SAN (7,5,3) is a traditional festival in Japan celebrated on 15th of November. Normally, 3 years old girls, 5 years old boys, and 7 years old girls go to a shrine and pray for good health and well-being. In the old days, children surviving to grow older was not as easy as today. Therefore, people wished for children to grow up healthy and celebrated their growth at the same time.

Its origin is the rite of passage in HEIAN era which consists with 3 rites, 『KAMIOKI』, 『HAKAMAGI』, and 『OBITOKI』.

『KAMIOKI』:3 years old boys and girls
In HEIAN era, children below 3 years old had their heads shaved wishing for good health and to prevent illnesses as a custom. When they became 3 years old, KAMIOKI ceremony was held to wish for a good long life. After this point, they started to grow their hair long.

『HAKAMAGI』:5 years old boys
5 years old boys wore a HAKAMA (Japanese traditional bottoms for males) for the first time and stood on a GO board (board game's board). Standing on the board meant wishing for them to control all sides and situations as a man. After this ceremony, they were to be acknowledged as young men.

『OBITOKI』:7 years old girls
Children wore a KIMONO without an OBI. Instead of OBI, the KIMONO had strings to tie up for a KIMONO not to come undressed. Wearing an OBI meant children to be acknowledged as an adult. 7 years old girls wore an OBI for the first time in this ceremony to become an adult.

SHICHI・GO・SAN is celebrated on 15th of November, and its origins are said to be a few. In EDO era, the SHOGUN TSUNAYOSHI, TOKUGAWA's first son TOKUMATSU had the KAMIOKI ceremony on 15th of November and it became a custom to have the ceremony on that day amongst BUKE (SAMURAI families). It then spread to general publics and became popular. As the former November was the time to thank gods for a good harvest and 15th being a full moon combined to be a very good day for the ceremony. Also, according to NIJYUHAKKU (an ancient calendar), 15th of November was the KISYUKUNICHI which people believed that demons do not walk around on this day. And 7+5+3=15 was believed to be just right for the ceremony to held on the day.

Now days the number of people celebrating SHICHI・GO・SAN for 3 years old boys' is increasing and having this event is decided up to each family choosing a day during September to November. Traditionally, the shrine to pray at was a patron deity of a local community, however some people choose a famous shrine today as it is photogenic. Also, some Christian churches accept people to have the ceremony now days. Traditions always tend to be arranged to suit customs and lifestyles trough development.


Reference: Kimono Muse
https://na-tu-re.com/shichi-go-san-meaning-history/