二天一流, read
niten ichiryū: the Niten school, the two-sword school of Miyamoto Musashi, which the Book of Five Rings teaches. The name is three words, not four. 一流 is one word,
a school, the way every school of the sword is a 流; and 二天,
two heavens, is not a description of a technique but Musashi's own name, the name he signed his paintings with and the name on the stone his son raised for him. So
Two Heavens One Style reads the four characters one at a time, and it is right as a title once the reader knows it is a name, the way one says the Yagyū school. In Musashi's own hand the school was 二刀, two swords: his memorandum for Lord Hosokawa, the Confucian Hayashi Razan's inscription on his portrait, and his son's stele all say so, and the Book of Five Rings as it survives says two swords five times and 二天 twice. The dictionaries hold that the name Niten was given after his death by his pupil Terao, from the master's Buddhist name, 二天道楽居士; the book survives only in his pupils' copies. Since then the school has been Niten and nothing else, in every dictionary and on every dojo's door, and the scroll brushes the school's name as the school has carried it. The English is William Scott Wilson's; Alexander Bennett gives
Two Heavens as One. 二天一流 literally means "Two Heavens One Style" and is composed of the
kanji 二 (read ni) meaning "two",
天 (read ten) meaning "heaven, sky",
一 (read ichi) meaning "one", and
流 (read ryū) meaning "style".