Kimon (demons' gate) means the direction of the northeast (ushi-tora; between the Ox (second sign of Chinese zodiac which means north-northeast) and the Tiger (third sign of Chinese zodiac which means east-northeast)). Yin-yang philosophy considers it as the direction where demons go in and out, and a direction that people should avoid. Unlike other directional spirits, the kimon is always positioned at ushi-tora.
The direction opposite the kimon, the southwest (hitsuji-saru; between the Ram (eighth sign of Chinese zodiac which means south-southwest) and the Monkey (ninth sign of Chinese zodiac which means west-southwest)), is called Urakimon (the back demons' gate), and people have an aversion for this direction as well.
Kimon is based on a story in a Chinese classic text "Shan Hai Jing" (Classic of the mountains and the sea), that defined the northwest (inui; between the Dog (eleventh sign of Chinese zodiac which means west-northwest) and the Boar (twelfth sign of the Chinese zodiac which means north-northwest)) as 'tenmon' (deva gate), the southwest (hitsuji-saru) as 'jinmon' (man's gate), southeast (tatsumi; between the Dragon (fifth sign of Chinese zodiac which means east-southeast) and the Serpent (sixth sign of Chinese zodiac which means south-southeast) as 'fumon' (wind's gate) and northeast (ushi-tora) as 'kimon.'
During the Edo period, when building a house or when noble people move, the direction of the kimon was considered to be best avoided. Furthermore, a peach tree was planted in the direction of the kimon or a monkey statue consecrated there as Kimon-sake (to guard against the kimon), since the opposite direction of the kimon is the Monkey (in Japanese 'saru' which is a homonym for the Japanese word 'expel'). There is a wooden statue of a monkey placed behind the roof at the northeast corner of the Kyoto Imperial Palace to block the kimon (which refers to Saru-ga-tsuji (literally, monkey's road)). Even now, there is still a strong custom against positioning any gate or storage room, or any place using water such as a kitchen, rest room, or bath, in the direction coinciding with the kimon as seen from the center of the house.
Also, in capital planning, Enryaku-ji Temple on Mt. Hiei was placed in Heian-kyo (the ancient capital of Japan in current Kyoto) in the direction of the kimon as seen from Daidairi (the Greater Imperial Palace), and Kanei-ji temple on Mt. Toei was placed in Edo in the direction of the kimon as seen from Edo-jo Castle.
Theories About the Kimon
In yin-yang philosophy, it is explained that the north and the west are regarded as yin, the east and the south as yang, and that northeast and southwest become unstable because they are the boundaries between yin and yang.
Other than the tradition that the kimon is to be avoided, another theory says that because it is the direction that spirits pass through, or the direction where the sun is born (the life gate), people have to guard their pure energy.
Another theory about the origin of the kimon is that because the prevailing wind blows from the northeast in China, inside a house any wet areas placed in that direction as seen from the center of the house would become unsanitary.
Kimon in Everyday Language
As mentioned above, the word kimon originally had a magical meaning, but it came to be used as a word referring to 'something that is likely to have an unpleasant result.'
It refers not only to the direction, but also to places, time zones, or particular subjects, and the range of its use is wide.