At the head of the line stands its founder, the smith who cut the single character 左 on his tang and is read in the published genealogies as Saemon Saburo, called O- or . The place him as the grandson of Sairen and son of Jitsua, the old succession of Ryosai, Sairen, and Jitsua whose steel ran sunken and rustic in a the school inherited from Yamato. Since the sword books he has been counted among the pupils of Masamune of , one of the Masamune Juttetsu, and the judges treat that - schooling as the pivot of his identity: against the provincial manner of his forebears he is the reformer who carried the idiom into Kyushu. His working life falls in the early period, and the single 左, often paired with 筑州住 on the reverse, becomes the founding mark from which the whole line takes its name. This is the apex generation, the work of O-'s own hand rather than the broader Sue- pupils who follow.
What the describe is a steel that runs bright and clear where the older Kyushu work ran dark. The is a well-knit , tight on the small and standing more open on the wide , carrying dust-fine thickly, abundant , and a faint ; the verdict recurs that and alike run limpid and , one judge noting steel that shows "absolutely none of the whitish cast or blackish tone" of lesser Kyushu work. Over that ground O- tempers a - mixed with and , the deep and the thick, with and entering and fine and drawn through the ; , , and appear on the broader blades. The is the structural signature the judges look to: it thrusts up () to a pointed tip, runs long , and returns at length. The are small, of thin and , with a withered () . Set against this, the later Sue- hands read as weaker and more standardized, their shallower and their less keen, so that O- stands alone for the force of his pointed and the brilliance of his steel.
For , the route attribution first through the and the point: the bright, clear free of whiteness is what separates an O- blade from its fellows when the thrusting, pointed alone will not, and the record divides cleanly into signed of flowing fine chisel and - papered . Signature works anchor the phase: the Kosetsu (江雪左文字), repeatedly named his only surviving signed and a National Treasure, and the Danjo in , held by the Uesugi house. Named run through the great families: the Onishi passed through the Doi and Tokugawa to Arima of Kurume, the Homoji to Tachibana of Yanagawa, others to the Owari Tokugawa, the Sendai Date, the Sakai of Himeji, and the Inaba; one recorded in the Kotoku Toezu was among the personal swords of the Taiko, Hideyoshi himself. The school is the place where the manner becomes a Kyushu one, and these blades are the record of that transformation in O-'s own hand.