This is Aikido, by Tohei
I was looking through my old copy of "This is Aikdio" by Tohei this weekend and once again I thought I'd recommend the book for any and all styles. If someone can get a foothold idea of how to use the jin/kokyu forces of "ki", this book by Tohei does a great job of explaining how the ki forces are used in a number of Aikido waza.
This book was published back in the late sixties before the split of Tohei from Hombu Dojo. IIRC, O-Sensei was still alive when the book was published.
When I bought the book, I thought it was cool, showed some good stuff, etc., but I didn't understand the magnitude of importance or even what the ki forces really were... so I simply missed how great this book is.
Nowadays, it's a very hard-to-find book.... mainly, I think, because the importance of it was never recognized since most westerners don't really understand the ki skills or, if they have some bits and pieces, they don't understand the excellent succinctness of the descriptions in this book for the serious Aikido practitioner.
My considered opinion, FWIW