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Ni-Ten Ichi Ryu

Musashi created and refined a two-sword kenjutsu technique called niten'ichi (二天一, "two heavens as one") or nitōichi (二刀一, "two swords as one") or ' Niten Ichi-ryū ' (A Kongen Buddhist Sutra refers to the two heavens as the two guardians of Buddha). In this technique, the swordsman uses both a large sword, and a "companion sword" at the same time, i.e. a katana with a wakizashi.

The two-handed movements of temple drummers may have inspired him, although it could be that the technique was forged through Musashi's combat experience. Jitte techniques were taught to him by his father—the jitte was often used in battle paired with a sword; the jitte would parry and neutralize the weapon of the enemy while the sword struck or the practitioner grappled with the enemy. Today Musashi's style of swordsmanship is known as Hyōhō Niten Ichi-ryū.

Musashi was also an expert in throwing weapons. He frequently threw his short sword, and Kenji Tokitsu believes that shuriken methods for the wakizashi were the Niten Ichi Ryu's secret techniques.

Within the book, Musashi mentions that the use of two swords within strategy is equally beneficial to those who use the skill for individual duels or large engagements. The idea of using two hands for a sword is an idea that Musashi opposes because there is no fluidity in movement with two hands: "If you hold a sword with both hands, it is difficult to wield it freely to left and right, so my method is to carry the sword in one hand." He also disagrees with the idea of using a sword with two hands on a horse and/or riding on unstable terrain, such as muddy swamps, rice fields, or within crowds of people.

To learn the strategy of Ni-Ten Ichi Ryū, Musashi asserts that by training with two long swords, one in each hand, one will be able to overcome the cumbersome nature of using a sword in both hands. Although it is difficult, Musashi agrees that there are times in which the long sword must be used with two hands, but one skillful enough should not need it.

After using two long swords proficiently enough, mastery of a long sword, and a "companion sword", most likely a wakizashi, will be much increased: "When you become used to wielding the long sword, you will gain the power of the Way and wield the sword well."

In short, it could be seen, from the excerpts from The Book of Five Rings, that real strategy behind Ni-Ten No Ichi Ryu, is that there is no real iron-clad method, path, or type of weaponry specific to the style of Ni-Ten No Ichi Ryu:

You can win with a long weapon, and yet you can also win with a short weapon. In short, the Way of the Ichi school is the spirit of winning, whatever the weapon and whatever its size.