A translation of key sections of the so-called Five Books of Shugen has been completed, including commentary on the Thirty-Three Sections. This will serve as a great anchor for study, alongside Dewa Shugen specific interpretations and oral traditions from the lineages.
The majority of what constitutes doctrine in Shugendo was formalised during the early Medieval period, alongside a major enmeshing with esoteric Buddhism, with sectarian perspectives developing much later on. Most early texts are collections of kirigami, that is, ritual-memoranda outlining longstanding reserved oral traditions based on direct transmission between master and disciple. These collections reveal Shugen's fundamental approach to these doctrines as well as being experiential (ritual) texts. Having been bound together in various forms, these went on to become some of the core texts which practitioners in the Edo period were expected to study. With Shugen often presented as a purely practice/experiential orientated tradition - or even worse, a tradition without any doctrine at all, it becomes vital that practitioners engage deeply with the fundamental texts and reliances of the sect, alongside the all-embracing outlook of the Mahāyāna.
As with other Buddhist sects in Japan, the majority of the modern priesthood is hereditary, fulfilling a primarily ritual function of servicing parishoners. This is to say, it is an assumption that priests have any real working knowledge of doctrine or advanced teachings, with ordination and kegyō coming as very much a first step in a practitioner's religious career.
While scholarly work on Shugen is now well-established, for practitioners, it is a requirement that proper engagement with this material requires the consultation, guidance and instruction of a qualified dai-sendatsu as well as appropriate initiation and empowerment (abhiseka).
A brief note on kūden: Most people want a transactional, on-demand standardised program to follow; a curriculum -- not a mentor-disciple relationship. I've witnessed more than a few fellow travellers throughout the Shugen world across the last 15 years who would have a tantrum because they had not been taught something simply because they requested it, or found that their lack of approach resulted in an equally lacklustre teaching. In an age of open-source esotericism, empty contrived ritualism, disembodied knowledge, AI influencer slop, scholarly cynicism, and (mis)information-saturation, I truly believe there is something fertile and vital in the framework of kūden, and the receiving of teachings with appropriate timing, maturity, apprenticeship, and context. In an age of obsession with priestly-rank and identity, there is also a climate of conceit and premature revelation, and I'm encouraged by the words of Dai-Ajari; 'It took twenty years of proper practice before I had anything worth saying..'. For more on this topic, see my translation of the work, "Tracing the Origins of Esoteric Buddhism."
"..In the end what is discovered is the quality of your own approach..."