Hand in hand with Shinkage Ryu, the Yagyu later absorbed an art of Iai as well which is taught in tandem at the Yagyukai. The first part of this article is taken from the Yagyukai site which is an informative reference and can be found here. The second part in italics is quoted from the kampaibudokai site.
Yagyu Seigo Ryu Batto-jutsu
Isahaya Chouzaemon Nobumasa learned the techniques of ju-jutsu and batto (sword drawing) from the monk Seigo, and created a school which he called Seigo Ryu. Isahaya's leading disciple, Kajiwara Genzaemon Naokage, passed Seigo Ryu down to the warriors of the Owari domain, and Nagaoka Fusahide, who played an active role as an assistant to the headmasters of Yagyu Shinkage Ryu Heihou, mastered the heart of Seigo Ryu Batto. In the following generation, Nagaoka Fusashige, another important figure in the history of Owari Yagyu Shinkage Ryu, continued to develop its theory and technique in accordance with the principles of Shinkage Ryu.
Yagyu Toshichika and Toshinaga polished Seigo Ryu Batto, and it has been passed down to Yagyu Koichi as Yagyu Seigo Ryu Batto.
William de Lange's book "Iaido"
In his book de Lange gives an outline of the kata (it should be noted this is a branch school). De Lange says the Yagyu had also drawn upon Sekiguchi Ryu and Rikishin Ryu Iai.
Yagyu Seigo Ryu Videos
The following is taken directly from the kampaibudokai site - the original article with further informaiton can be found here.
The Yagyu Shinkage ryu was founded by Sekishusai in the beginning of the Edo period, so there are no techniques implying armour, no tate hiza, and nukitsuke is a cut only on exception. Mostly it's taking a defensive posture. Only if the bad guy insists does he get a beating. At the moment there are about 100-200 students of this ryu in Japan. There are 43 iai kata with no particular order, but 7 are considered basic. Cuts use only the tip, so the cuts never stop (never touch bone) but are part of a flowing movement. One will often shift back near the end of the cut as a defensive move. A Yagyu suburi demonstrated by sensei is making big circles (or figure 8's) from left hasso to right waki to right hasso to left waki, while changing feet. (sorry about the poor description) Cuts are made using the muscles of the back, not the arms.
Properly speaking, Shinkage-ryu does not contain iaijutsu techniques, it is strictly a school of hyoho (or heiho, i.e., martial strategy) and kenjutsu. However, the Yagyu Shinkage-ryu line has subsumed the battojutsu of Yagyu Seigo-ryu, a school derived from Seigo-ryu jujutsu (and some jojutsu techniques developed by Yagyu Jubei Mitsutoshi). Also, present-day Yagyu Seigo-ryu battojutsu waza are a reconstruction of the original techniques, probably at the end of the Meiji era, by Yagyu Toshichika (Genshu) and his son, Gencho.
Originally, Seigo-ryu was a jujutsu ryu that was practised in the Owari han (domain). The founder was a man named Mizuhaya Chozaemon Nobumasa, who was also involved (perhaps the founder) of Ippon-ryu. It was a jujutsu ryu, but it also included iai and hojojutsu (rope-tying, a common adjunct to jujutsu ryu).
Back in the late 1700s, the then-headmaster, Nagaoka Fusashige (Torei), was an assistant instructor (shihan hosa) of the then-head of the Shinkage-ryu. He was a very exceptional man as a scholar, administrator *and* swordsman, and he took voluminous notes on what he'd learned. He incorporated Shinkage-ryu principles and training methods into Seigo-ryu and created a number of techniques of sword-drawing, which we refer to over-all as battojutsu. Seated techniques are called iai, the standing techniques are tachi-ai batto.
Yagyu Seigo Ryu Batto-jutsu
Isahaya Chouzaemon Nobumasa learned the techniques of ju-jutsu and batto (sword drawing) from the monk Seigo, and created a school which he called Seigo Ryu. Isahaya's leading disciple, Kajiwara Genzaemon Naokage, passed Seigo Ryu down to the warriors of the Owari domain, and Nagaoka Fusahide, who played an active role as an assistant to the headmasters of Yagyu Shinkage Ryu Heihou, mastered the heart of Seigo Ryu Batto. In the following generation, Nagaoka Fusashige, another important figure in the history of Owari Yagyu Shinkage Ryu, continued to develop its theory and technique in accordance with the principles of Shinkage Ryu.
Yagyu Toshichika and Toshinaga polished Seigo Ryu Batto, and it has been passed down to Yagyu Koichi as Yagyu Seigo Ryu Batto.
William de Lange's book "Iaido"
In his book de Lange gives an outline of the kata (it should be noted this is a branch school). De Lange says the Yagyu had also drawn upon Sekiguchi Ryu and Rikishin Ryu Iai.
Yagyu Seigo Ryu Videos
The following is taken directly from the kampaibudokai site - the original article with further informaiton can be found here.
The Yagyu Shinkage ryu was founded by Sekishusai in the beginning of the Edo period, so there are no techniques implying armour, no tate hiza, and nukitsuke is a cut only on exception. Mostly it's taking a defensive posture. Only if the bad guy insists does he get a beating. At the moment there are about 100-200 students of this ryu in Japan. There are 43 iai kata with no particular order, but 7 are considered basic. Cuts use only the tip, so the cuts never stop (never touch bone) but are part of a flowing movement. One will often shift back near the end of the cut as a defensive move. A Yagyu suburi demonstrated by sensei is making big circles (or figure 8's) from left hasso to right waki to right hasso to left waki, while changing feet. (sorry about the poor description) Cuts are made using the muscles of the back, not the arms.
Properly speaking, Shinkage-ryu does not contain iaijutsu techniques, it is strictly a school of hyoho (or heiho, i.e., martial strategy) and kenjutsu. However, the Yagyu Shinkage-ryu line has subsumed the battojutsu of Yagyu Seigo-ryu, a school derived from Seigo-ryu jujutsu (and some jojutsu techniques developed by Yagyu Jubei Mitsutoshi). Also, present-day Yagyu Seigo-ryu battojutsu waza are a reconstruction of the original techniques, probably at the end of the Meiji era, by Yagyu Toshichika (Genshu) and his son, Gencho.
Originally, Seigo-ryu was a jujutsu ryu that was practised in the Owari han (domain). The founder was a man named Mizuhaya Chozaemon Nobumasa, who was also involved (perhaps the founder) of Ippon-ryu. It was a jujutsu ryu, but it also included iai and hojojutsu (rope-tying, a common adjunct to jujutsu ryu).
Back in the late 1700s, the then-headmaster, Nagaoka Fusashige (Torei), was an assistant instructor (shihan hosa) of the then-head of the Shinkage-ryu. He was a very exceptional man as a scholar, administrator *and* swordsman, and he took voluminous notes on what he'd learned. He incorporated Shinkage-ryu principles and training methods into Seigo-ryu and created a number of techniques of sword-drawing, which we refer to over-all as battojutsu. Seated techniques are called iai, the standing techniques are tachi-ai batto.