I didn't know much about Japanese architects until I took a class on "The Metabolists" in grad school and I was hugely inspired. The class was by one of my favorite professors and that, combined with the content learned was maybe one of the most enjoyable architecture classes I had taken. It was a perfect mix of history and philosophy. Lots of class discussions and things like that.
The book that we used as our main text is called Project Japan: Metabolism Talks. It was actually written by Koolhaus (in addition to a few other). It isn't a textbook...more of a collection of history, interviews, specific projects. Its a beautiful book and I still thumb through it all the time. I would highly recommend it to anybody in the field, especially if you don't know much about modern Japanese architecture.
I took a class on metabolism in grad school and it was one of THE best classes I took. I learned so much about something I didn't know too much about previously, and the professor was excellent.
The textbook we used is by Koolhaus and its a beautiful book for anybody looking to add to their collection!