Shakuzetsu-nichi Day (an unlucky day) (赤舌日)

Shakuzetsu-nichi Day is a day controlled by Rasetsu-shin God (type of evil spirit) of Onmyodo (way of Yin and Yang) (in the customs of nobles and ordinary citizens), and was considered unlucky day.

In Onmyodo, it is said that Shakuzetsu-jin God (Guardian god at the west gate of Oto [imperial capital] of Taisai-jin God [spirit of Jupiter]) employs six Kijin (demon-gods) to send one by one every six days to protect.

The six Kijin employed by Shakuzetsu-jin God (the six great Kijin)
The first Kijin: Myodo-shin God
The second Kijin: Chiko-shin God
The third Kijin: Rasetsu-shin God
The fourth Kijin: Daitaku-shin God
The fifth Kijin: Byakudo-shin God
The sixth Kijin: Rogokuju-shin God

Due to the high-handed behavior of one of the Kijin employed (the third Rasetsu-shin God), it is said that it had better not to hold such event as weddings and celebrations on the day of the Kijin which comes every six days. That custom started by priests and became popular especially in the Heian period. At the present time, people are little conscious of this Shakuzetsu-nichi Day (an unlucky day) and most people do not know the existence of such days.

Kenko YOSHIDA wrote about Shakuzetsu-nichi Day in the 91st passage of Tsurezuregusa (Essays in Idleness).

The Onmyodo teachings have nothing to say on the subject of Shakuzetsu-nichi Day.
(The rest is omitted)

Kenko Hoshi wrote 'A wicked deed performed on an auspicious day will certainly prove ill-omened.
A good deed performed on an unlucky day will certainly prove auspicious.'
He criticized the then customs to avoid Shakuzetsu-nichi Day in relation to his own view of life as something transient and empty.

Shakuzetsu-nichi Day together with Shakko-nichi Day is thought to have influenced folk belief of Rokuyo (a recurring six-day series of lucky or unlucky days that is incorporated into the Japanese calendar) one way or another.