During the Heian period Nikko-san
(Mt. Nikko, -san here means mount or mountain),
Nasu-san (in Tochigi Prefecture)
and Haguro-san(Yamagata Prefecture)
were well known as areas where the hard training
for mountain priests (Yamabushi) took place.
The mythic being Tengu also lived in these mountains.
A legend tells that one day Tengu was going from Nikko-san
to Haguro-san,when he decided to take a rest.
Sitting against a large rock on Nasu-san he noticed
hot water coming from under the rock, so he lifted it up
and threw it aside.
The hot water rushed out,
from then on being known as an onsen or spa pool.
Tengu and reverence for or worship
of mountains were basics of the training
for the mountain priests (Yamabushi) living and training in the mountains.
They formed their own grouping completely apart from those governing Japan.
At the beginning of the Tokugawa Shogunate there were about 60,000 people
living in the mountains as Yamabushi.
Tokugawa was alarmed by the large size of this group, not under his power
So Tokugawa Ieyesu took steps to break up this grouping,
he banished or deported the leaders of it and wiped out the rest.
At this time he founded Toshogu shrine in Nikko to counter the worship
destroying the training and worship centers of the Yamabushi at the same
The Kurabane-han (region controlled by a daimyo or duke) took control
of the Nikko
and Nasu region to destroy Tengu worship and the Yamabushi