September 23rd: 秋分の日 (Autumnal Equinox)

September 23rd in Japan is Shuubun-no-hi (Autumnal Equinox).

In Japanese custom, a seven-day period called higan occurs during the time frame of the autumnal and vernal equinoxes (three days before and after the equinox). In Buddhist context, higan means the “other side of the river of death” the place where those who have passed away dwell. During this time, people visit their family graves praying their respects by cleaning the gravestones with water and brush, offering food and flowers, and praying.

The national holiday was established in 1948, but previously it was a day to venerate the deceased imperial line in a festival known as Shūki kōrei-sai (秋季皇霊祭). Kōrei-saishi means “veneration of the imperial spirits” and the rites are performed by the imperial family inside the Hall of Imperial Ancestral Spirits in the Imperial Palace. Before the Meiji Restoration, the Imperial family started to gain more and more popularity, and Imperial tombs in decay were repaired and became vehicles for a more spiritualized connection with the nation-state. When Japan instated the solar calendar, Shūki kōrei-sai was added to the Kōrei-saishi, a part of the Ordinance of Imperial House Rites. These rites were later terminated in 1947.

Reference: http://eos.kokugakuin.ac.jp/modules/xwords/entry.php?entryID=735