Ah good ol Empty Fort strategy. It's from Chinese internal wars rather than the Sengoku period of Japan. This version is based on Zhuge Liang in Romance of the Three Kingdoms who ordered his soldiers to disguise themselves as civilians and open the gates of his city making it appear defenseless and played his guqin when the opposing Wei army arrived. Zhuge Liang also had the reputation for not taking risks so the strategy worked in that book the same way and for the same reason it does here
