Start with high-confidence martial arts books, then narrow by subgenre or adjacent topics.
Ninja
John Man
I Was an Eighth-grade Ninja
Andrew Simmons, Rob Corley
Tap Out
Eric Devine
Jet Black and the Ninja Wind
Leza Lowitz, Shogo Oketani
The Book of Five Rings
Miyamoto Musashi, Shiro Tsujimura
The Unfettered Mind
Takuan Soho, William Scott Wilson
The Legendary Mo Seto
A. Y. Chan
