According to the Taoism, which started in China, we, humans have three bugs inside our body; one in our head, another in our internal organs and third one in our lower part of the body. Those bugs are called SAN-SHI.
These SAN-SHI, are believed to cause headaches and stomachaches and others, but not only that, they come out of our bodies on the night of the KOSHIN. On the night of the KOSHIN, which has a sixty nights cycle, these SAN-SHI, report our bad behaviors to TENTEI, the god.
TENTEI, the god that is believed to preside over human lives, decides our lifetime, according to those reports he receives from SAN-SHI.
To avoid the SAN-SHI from reporting our deeds to god, we stay awake all through the night and watch out for these bugs, so that they do not leave our bodies - this is called the KOSHIN-KO.
This KOSHIN-KO, is passed from China during the 8th century (Nara era), and was done by noblemen back during 12th century (Heian era). By 17 thru 19th century (Edo era), this was linked with Buddhism and Shinto, it spread and became popular among the general public.
And now, remains of the KOSHIN can be seen from all the tumulus and steeples that are through out Japan.
TOKYO KOSHINDO is a group of people who practices and helps the revival of KOSHIN-KO.
Address: Mukoujima 3-7-4 Sumida-ku, Tokyo