Boryaku(謀略,Boryaku?) is one of the 18 fundamental skills of the Togakure-ryū school of ninjutsu. The Togakure ryu is a ninjutsu ryuha that was founded, according to Bujinkan, about eight hundred years ago by Daisuke Nishina (Togakure), who learned shugendo practices as well as hakuun ryu ninjutsu from Kagakure Doshi. ... Ninjutsu ) sometimes used interchangeably with the term ninpÅ ), it is the martial arts practiced by the shinobi (also commonly known as the ninja). ...
Alongside more orthodox and mainstream measures, Boryaku includes use of unorthodox strategies and tactics, as well as manipulation of politics and exploitation of other current events to assist in subtle influence of the opponent. This article is about real and historical warfare. ... Military tactics is the collective name for methods of engaging and defeating an enemy in battle. ...
Sources
Dr. Hatsumi, M. (1981) Ninjutsu: History and Tradition. Burbank, CA: Unique Publications. ISBN 0-86568-027-2
In the third chapter of the treatise, which title can be translated as "Strategic attack" (N.I.Konrad) or "Attacking by stratagem" (L.Jales), it is saying: "Hundred times to fight and hundred times to win - not the best from the best; the best from the best - to defeat enemy's army without fighting" (N.I.Konrad: Cinology.
By strategic attacking, or attacking by sratagem (in japanese - "boryaku", "bokei" - "ruse, manoeuvre, intrigue, plot, cunning plan").
In the middle of Dannoura's battle, the critical battle of Teira-Minamoto's war, Ava-no Shigeyoshi, "bought" by son, changed a side and became fought for Minamoto, and Taira were defeated.