Yagyū Shingan-ryū (柳生心眼流?), is a traditional school (koryū) of Japanese martial arts. Different styles of Yagyū Shingan-ryū, such as Heihojutsu and Taijutsu, assert different founders, Takenaga Hayato and Araki Mataemon respectively, but they all go back to Ushū Tatewaki (羽州 帯刀), referred to in some historical scrolls as Shindō Tatewaki, who taught a system based on Sengoku-period battlefield tactics, that was called Shindō-ryū.
The word shingan (心眼?) is rooted in Zen philosophy, and was chosen to describe a fundamental concept of the style. Shingan means "mind’s eye," or "heart's eye," and refers to the ability to sense or read an opponent's intentions via an inner sense. Originally called simply Shingan-ryū, it was later renamed Yagyū Shingan-ryū, due to the influence of Yagyu Tajima No Kami Munenori's Yagyū Shinkage-ryū.
Yagyū Shingan-ryū was created to be a battlefield art with a large comprehensive curriculum of weapons, and grappling techniques for use both while armored and unarmored. The techniques of Yagyū Shingan-ryū were therefore designed to eliminate an enemy quickly and effortlessly. In the early days, both the Yagyū Shingan and Shinkage schools were similar, as both consisted of an array of armed and unarmed combat techniques. However, as the two schools evolved, the Yagyū Shinkage-ryū focused primarily on swordsmanship (kenjutsu), whereas the Yagyū Shingan-ryū continued as a comprehensive combat system, training several arts, including jujutsu, quarterstaff fighting (bōjutsu), glaive fighting (naginatajutsu), sword drawing techniques (iaijutsu) and sword fighting (kenjutsu).
Read more about Yagyū Shingan-ryū: Takenaga Hayato, Araki Mataemon