(Japanese) The secret teaching, esoteric Buddhism.
There are five general areas taught in Tendai Buddhism. They are the teachings of the Lotus Sutra; esoteric Mikkyô practices; meditation practices; precepts; and Pure Land teachings.
This form of Buddhism reached Japan at the beginning of the 9th century. There is a clear connection between Mikao Usui’s teachings and Mikkyô. For example: the physical aspects of the reiju called Go Shimbô and the origins of the fourth jumon DKM.
If, as is claimed, Mikao Usui was a Tendai lay priest, he would have studied Mikkyô as it is an integral part of Tendai Buddhism.