In the Edo Era (1603 - 1867 A.D.) Koshin-Machi became more popular in other levels of society and with commoners, and the festivities took more the character of a belief. It was at that time that deities started to appear within the faith. One was Shoumen-Kongou, a fearsome blue faced deity with many arms. Shoumen-Kongou is enshrined at the Naramachi Museum.
The main Koshin belief that survived from an original complex faith, is the concept that three worms, called Sanshi, (三尸) live in everyone's body. The Sanshi keep track of the good deeds and particularly the bad deeds of the person they inhabit. On the night called Koshin-Machi (which happens each 60 days), while the person sleeps, the sanshis leave the body and go to Ten-Tei (天帝), the Heavenly God, to report about the deeds of that person. Ten-Tei will then decide to punish bad people making them ill, shortening their time alive and in extreme cases putting an end to their lives. Believers of Koshin will try to live a life without bad deeds, but those who have reason to fear will try to stay awake during Koshin nights, this is the only way to prevent the Sanshi from leaving the body and reporting to Ten-Tei.
Shoumen-Kongou became Koshin-san when people expected this demon to make the Sanshis themselves ill and prevent them going to Ten-Tei. Shoumen-Kongou is not really a god but a demon who can send illnesses.
Three monkeys covering eyes, mouth and ears with their hands are the best known symbols of Koshin faith. They are Mizaru (not see), Iwazaru (not say) and Kikazaru (not hear). It is not very clear why the three monkeys became part of Koshin belief, but is assumed that it is because like the monkeys, the Sanshis and Ten-Tei are not to see, hear, or tell the bad deeds of a person.
Statues of Shoumen-Kongou with the three monkeys have existed in temples and shrines since the Edo era. Sometimes carved stones that took the name Koshin-do were placed around a dwelling for protection. Such stones can present diverse forms, from having only Chinese characters (kanji) to including a depiction of Shoumen Kongou with one, two or three monkeys.
Koshin Stones have almost vanished, victims to roads and vandalism, but some people try to save them and relocate the stones to temples or shrines.
Other custom of the Koshin belief are the use of paper scrolls also showing Koshin-san and the monkeys which are displayed on Koshin-machi, the Koshin night. Those who keep this tradition invite neighbours, friends and relatives and sit in front of a provisory altar which has a bowl of rice, soup, seasonal fruit, flowers, candles and incense sticks. They also hang scrolls with pictures of Shoumen Kongou. Everyone will try to stay awake through the whole night.