Niten Ichi-ryū
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, such as a katana with a wakizashi.