Higan-e (meeting of equinoctial week) For seven days, on the day of the imperial ceremony of ancestor worship formerly held on the vernal or autumnal equinox and three days before and after that

After he spent 6 years of his ascetic practices, he saw the morning star under the linden tree in Bodh Gaya and he obtained enlightenment more than ever and finished his practice Buddhism, so that we are going to celebrate and hold a memorial service called, 'Jodo-e'.
In Zen Buddhism, this is celebrated by continuing zazen from December 1st to early morning on December 8th.
This is called "Rouhatsusessin" which means zazen in December.