Hyoho Niten Ichi-ryu or more correctly Hyoho Niten Ichi-ryū (二天一流), can roughly be translated as "the school of the strategy of two heavens as one". It is classified as a koryū (ancient school) (to learn more about the differences between koryū and gendai arts such as Kendo, Karate etc please check out this article - What is Koryu).
The style, famous for its simultaneous used of two swords (the katana and wakizashi, known in the style as the daitō and shoto respectively), from which it derives its name, was conceived of and developed by Miyamoto Musashi (宮本 武蔵), a famous samurai, artist, poet and author. He is well known in the West for his book on strategy; Go Rin no Sho (Book of 5 Rings).
You can read more about Musashi - here.
Hyoho (meaning strategy also spelt Heiho) Niten Ichi Ryū is a form of Kenjutsu (剣術) meaning "the method, or technique, of the sword." This is opposed to kendo, which means "the way of the sword". Kenjutsu is a catch-all term for all (koryū) schools of Japanese swordsmanship, particularly those that predate the Meiji Restoration (1868). In this way kenjutsu is very much associated with the genuine battlefield techniques used by the samurai during combat in feudal Japan.
Hyoho Niten Ichi ryū is unique among kenjutsu styles as it focuses on the one handed use of the sword, be it the long sword (daitō) or short sword (kodachi). Musashi felt that there was limited flexibility and fluidity of movement when both hands are used on a single sword. In his writings Musashi indicates that a sword was held in both hands is not easy to wield freely to either side, nor is it ideal for use when mounted on horseback.
Thus at roughly the age of 21 (1604-1605), he started developing a two sword style of combat, allowing the swordsman to wield one sword in each hand fluidly. He had already established himself as an excellent swordsman in various duels and battles (Kihei, Akiyama, Genzaemon, Sekigahara etc). However he did not use it in public combat until he was 30-31 between 1614 and 1615, after the Winter and Summer battles of the Osaka campaign during a duel against Miyake Gunbei.
Musashi fought over 66 duels and won them all and he founded a number of schools of swordsmanship culminating in the Hyoho Niten Ichi Ryū.
Musashi's Niten technique was counter intuitive to the traditions of most swordsmen of the time as the majority of schools were based on gripping the katana with both hands. In addition Musashi’s technique was highly sophisticated and refined, focused on efficient movement and power. To achieve this the style has no flashy, excessive or unwanted movements. Instead it focuses on developing subtle timing and distance removing the swordsman from immediate danger while simultaneous creating an opening to strike the opponent.
Hyoho Niten Ichi Ryū kenjutsu is comprised of the following techniques:
Today the following sets of techniques (waza or kata) are transmitted:
1) Tachi Seiho (太刀勢法): Twelve techniques with long sword:
2) Kodachi Seiho (小太刀勢法): Seven techniques with a short sword:
3) Nito Seiho (二刀勢法): Five techniques with two swords corresponding to the five forms in the Water Scroll of the Go No Rin Sho:
4) Bōjutsu (棒術): Twenty techniques with a long staff bō (including 7 Bō Vs Bō techniques and 13 Bō Vs sword techniques).
5) Aikuchi roppo - Six waza with a knife/grappling (yawara)
6) Jitte to jutsu—Five techniques against a sword
I'll be discussing Hyoho Niten Ichi Ryu a little more on the site, and reviewing the weapons used in the style itself as I have been given permission by Takanori Kajiya Soke, 12th headmaster of the Hyoho Niten Ichi Ryū to study the style in more detail.