Not many people like to admit it, but this has been the number one book on Ninja Meditation for 20 years. It goes in depth into many different aspects of the Ninja's meditation techniques, covering things you can't really find in other books. It covers breathing excersises, Kuji Kiri, Elemental meditation, internal strength, cultivation and circulation of ki, mental powers, and much more. Anyone interested in this the mind techniques of the Ninja should take a look at this book. Just remember that this book won't teach you how to look into someones eyes and control them. It concentrates primarily on controlling your own mind. Think about how important that is. If you can control your own mind, you can choose wheather or not to be scared when attacked, you can choose when to be angry, or calm, etc. It is truley an intersting thing, controlling your own mind.
Grandmaster Kim also has a very unique form of writing, making the book quite interesting for all readers, serious or not.