There is always a training theme that is set by Soke Hatsumi at the beginning of year and this year is no exception. This year the feeling for the year is Kannin Doshi - perseverance of mutual respect. Respect yourself and respect your opponent. Muto dori and women's self defence are the physical aspects of training again this year. Basics like the Kihon Happo are also very important, especially for the 15th dans. All 15th dans must be able to demonstrate good basic technique.
There has been some discussion on social media around knowledge of the basics; kihon happo, san shin no kata, taihenjutsu and ukemi. Bujinkan dojo are supposed to work from the Ten Chi Jin, a syllabus that details this and other techniques to develop taijutsu and use of weapons. The standard for shodan at Bujinkan Newbury Dojo is to be able to correctly perform fundamental kihon happo, and san shin no kata and to be able to demonstrate variations. As well as the kihon of hanbo, bo staff, sword kamae and muto dori (as well as randori practice).
There can be an expectation that there are secret techniques that only senior grades know, or that some techniques are only shown to a few. But realistically there is only kihon happo and san shin no kata - its the application and understanding of the underlying principles that appear to be higher level techniques.
Without proper foundations in kamae and practice equally, there can be no development. It takes repeated practice over years - and there is always an opportunity to learn something new about the most fundamental of movements.
With reflection and experience comes insight. I have learned from my seniors and my students alike. Sometimes a simple question of "Why this way here and not move like this?" or "What if I did this though?" leads to a light bulb moment as you explain to a student; and gives you a better understanding of why the kata are the way they are. The longer you study them the deeper you understand them.
These kata have survived nigh on 1,000 years of development for a reason - they work in being the most efficient way to transmit principles. Realistically if you have to teach a complete comprehensive fighting system in secret then having 13 kata do all this is remarkable and fairly awe inspiring.