From: Ryōi Shintō-ryū Wa-jutsu Shinohara Shinichi (良移心当流和術 篠原信), Tenri University Academic Bulletin (天理大学学報) 212:35-42,20 (2005)

"It appears that from the time that Fukuno Shichirōuemon (福野七郎右衛門) was training with the Yagyū mon (柳生門 - Yagyū school), he was using the name Ryōi Shintō-ryū (良移心当流 ), and that for this method, he also mastered the ‘Jū no ri ‘ (柔の理 - pliant principle) inherent in the ‘Ken no ri’ (剣の理 - sword principle) of Yagyū Shinkage-ryū (柳生新陰流) while training in the ‘Torite’ (捕手 - capturing) of the ‘Soto no mono’ (外の物 -outside things), and aimed to perfect the style of the technique by innovatively adding aspects to Ryōi Shintō-ryū. This was such an excellent technique that it was endorsed by the two masters Yagyū Sekishūsai Munetoshi (柳生石舟斎宗厳) and Tajima no Kami Munenori (但馬守宗矩) as being an unparalleled secret art. 

In the Keichō era (around 1600), it is said that Fukuno Shichirōuemon took instruction from Munetoshi, taught Yagyū Shinkage-ryū to the attendants of Tokugawa Ieyasu (徳川家康) and was a person who achieved the rank of ‘Tatsujin’ (達人 - master, expert) as a martial artist. Although the foundations of Ryōi Shintō-ryū were the grappling techniques passed down from ancient times, it is undeniable that the “Jū no ri’, that is to say, the ‘Torite’, inherent in the “Soto no mono’ when training in the aforementioned Yagyū Shinkage-ryū was a factor in the perfection of the exquisite techniques of modern Jūjutsu (柔術)."

Pictures - Shogun Tokugawa Ieyasu (Wikipedia) and Peter King teaching Ryōi Shintō-ryū sword on seminar (25th - 26th Sept. 2021)