This is not the sort of book that you sit down and read straight through. It's not a training manual, not a "how to" ready-made recipe book for ninja enthusiasts. In fact, if you haven't seen Hatsumi or his better students train, then much of this may be plainly unintelligible. In this way it is reminiscent of the densho of old- they only make real sense to the initiated (something I suspect is at play in nearly all of his books, especially the ones with lots of photos and diagrams). Rather, it is a collection of related (and unrelated) snippets into the teaching and training philosophy of Hatsumi.
Topics include themes on fighting multiple attackers, use of blades, foot work, throws, training diligence, the transmission of the essence of the art and much more. There are also nice caveats in the text devoted to the perspectives of his top students.
While I mentioned that the point of the book is not instructional in the "step here and pull here" sense, it certainly would be a welcome addition to most martial artists' reading lists and is instructional on a deeper level, if you have the ability to see and understand.
And this brings up the point of yugen, that mysterious realm of life that isn't quite understood, but rather experienced. Much of this book reminds me of the intuitive approach we must have in our training. I find myself reading parts over now and again and each time I draw something else out. Like an icon or a great novel, it speaks freshly every time. Understand? Good. Play!
Gambatte!