A new book on Wasan has been published titled “Wasan, the Fascination of Traditional Japanese Mathematics” by Sakurai Susumu.
I was kindly sent a copy of this book. It provides a much needed updated introductory text in English on Wasan – with the only other work currently available being Smith and Mikami’s “A History of Japanese Mathematics” published over a century ago. However, it does not add anything new for those knowledgeable of the field, and touches very little on Sangaku. However, I do recommend it as a basic introduction to Wasan in English.
You can find a copy of the book on amazon.com here.