Much of what Japanese Zen is today, is greatly shaped by one manusciript, the essey title Bendōwa, claimed to be written by Dogen.
This document was found in a Kyoto temple during a very turbulent time in Japanese history, The
Meiji Restoration, in Japanese history, the political revolution in 1868 that brought about the final demise of the Tokugawa shogunate (military government)—thus ending the Edo (Tokugawa) period (1603–1867)https://en.wikipedia.org/wiki/Bend%C5%8Dwa
Bendōwa, a manuscript claimed to have been written by Dogen was found during this time. The claim is that it was found in a Kyoto temple in approximately 1661.
The manuscript primarily serves to introduce zazen 坐禅, or seated meditation, to Japanese Buddhists, very few of whom would have been exposed to the practice. Sourcehttps://en.wikipedia.org/wiki/Bend%C5%8Dwa
This manuscript is really important in that it sets the tempo for modern Japanese Zen, and how Zen is practiced here in the west.
It is likely that the manuscript is a fake, though there is no conclusive evidence to support this, as there is no evidence to indicate that Dogen actually wrote this.
Given that no Zen monk practiced seated meditation in Japan when this manuscript was found, and the practice only started much later after the discovery of the manuscript `mid 17th century, this manuscript should be set-aside as apocryphal.
Dogens own temple was short-lived. After his death the temple was nearly abandoned and absorbed by Keizan who brought Soto to Japan.
The zazen cults in my view most likely began out of Zen being smashed during the Meiji Restoration, in where much of the manuscripts where lost.
Japan has 4 anti-buddhist movements Haibutsu kishaku and during these times temples are destroyed, monks killed, manuscripts burnt.
It is estimated that 40,000 Buddhist temples were destroyed in Japan during this disastrous nationwide anti-Buddhist mayhem, and in certain places the percentage of Buddhist temples destroyed reached 80%https://en.wikipedia.org/wiki/Haibutsu_kishaku
With the temple system smashed, and what remained of them handed to prominent families to ‘take control’, it is likely that many cults existed and some still remains. There is a large Kanzion cult in Japan, and I even know of a Kanzion temple in Las Vegas that services this cult.
Interesting that Bendowa suddenly is found during these very turbulent times, and when the edicts of the Meji reforms came down. This more another strong evidence that the manuscript may in fact be a forgery.