Heiho Yukan Scroll #12
There are 9 clauses for mastering castle control. I will reveal these through my words.
#1: The matter of easily (re)gaining allies’ trust by taking a large force to attack a castle in another territory, which is normally a difficult feat
Let’s take into consideration the secret teachings of castle control from Koshu ryu. Baba Mino no Kami was able to share with the new generation the means to master this within the Koyo Gunkan, as inscribed to him by Yamamoto Kansuke Nyudo. The purpose of this document was meant to aid Takeda Shingen. – Castle control is relevant, as it is explained by Dokisai (nickname of Yamamoto Kansuke) through his solutions. Consequently, the talented Baba Mino no Kami upheld the teachings, which in turn became the method for fortification. It is also called “Kiyome no Shiro” (Castle Purification). Moreover, in the fields of Koyama Nyusen in Toshuu (present day Totomi Province), Nobufusa taught fortification to its entirety. Thus we have arrived, in present day, where the lessons of fortification can be shared from the information gathered through past experiences.
#2: The matter regarding a smaller force besieged by a larger army will not feel confined within a castle, but a larger force besieged by a smaller army will have no room to maneuver inside a castle