This is some of the best historical fantasy cum East Asian martial arts and warfare writing ever written. It covers the Muromachi period and the run up to the seizure of power of Hideoyshi in Japan, and involves warfare there and in China versus the Mongols.
This is an absolutely enchanting book that rises above its genre. If you know a little bit of the real history of the period it only becomes more fascinating. And if not, you’ll want to learn more.
The book is sadly out of print, and Robert Shea is now dead.