Syakkonichi (Shiyakukonichi) (赤口日)

Syakkonichi (Siyakukonichi) is the day ruled by Hachigokusotsushin (Hachigokusosshin) of onmyodo (way of IN and Yang), and thought to be the bad luck day for kuji (public duties), suit and contract.

In onmyodo, it is said that Shakkojin (the guardian god of the east gate of the capital of Taisaijin [the god of Jupiter]) employs the eight fierce gods, and guards the gate by sending one of them in turn a day in a eight-day cycle.

The eight fierce gods employed by Shakkojin (Hachidaiki)
The first fierce god: Tokeirashin
The second fierce god: Makeishurashin (Makeishiyurashin)
The third fierce god: Engokujushin (Engokujiyushin)
The fourth fierce god: Hachigokusotsushin (Hachigokusosshin)
The fifth fierce god: Katsumataijin
The sixth fierce god: Enrasetsushin (Enrasesshin)
The seventh fierce god: Raidenkoshin (Raidenkuwaushin)
The eighth fierce god: Komokutoshin (Kuwaumokutoshin)

In these eight days, because the one of the employed fierce gods (Hachigokusotsushin, the fourth fierce god) is the inauspicious god with eight faces and eight arms, its day is made Shakkonichi and thought to be the bad luck day.

It is thought that Syakkonichi, with Shakuzetsunichi (the day ruled by Syakuzetsujin [the guardian god of the west gate of the capital of Taisaijin]) had some influence on the present folk belief in Rokuyo (literally, "six days," the traditional six days in Japanese calendar).