From the 'Budo no densho' (武道の傳書 - “Handbook of martial arts) by Watanabe Ichiro (渡邉一郎), a Professor at the University of Tsukuba (筑波大学):
He (Fukuno Shichirouemon Masakatsu) learnt the military principles (兵法 Heihō) of the Shinkage ryū (新陰流) from two people (father and son): from father called Yagyū Munetoshi and from his son Munenori and he mastered the deep and secret essence of those principles at such extent that he was able to acquire the principle of the Yawara (和) and to establish a school that he named as Ryoi Shinto yawara (良移心當和), in the March of 1622."

Picture - statue of Yagyū Munenori