Miyamoto Musashi is traditionally credited with creating the two-sword Niten Ichi-ryū school.
Niten Ichi-ryū, often translated as “Two Heavens as One,” is associated with Musashi’s method of using a long sword and a short sword together. Musashi argued that a warrior should be able to use both hands and should not become rigidly dependent on one weapon or stance. The school is also called Niten-ryū in some contexts.
Musashi’s approach formed part of a wider Japanese martial tradition rather than a universal samurai fighting style. Different schools specialized in different weapons, techniques, and teachings, including spear, naginata, archery, and unarmed combat. The school’s ideas are also connected with Musashi’s Book of Five Rings, but the book and the school are not identical things. Later lineages preserved and developed the tradition.