Seki (関), in Province, grew from two roots set down in the period and rose to become the great center of mass sword production in the late medieval age. The published sources trace the wellspring of swordmaking to Kinju (whose name the commentary also reads Kaneshige), counted since antiquity among the Masamune Jittetsu, the ten disciples of Masamune, and to Kaneuji of the line; the Kokon Meizukushi records Kinju as a native of Tsuruga in who "crossed over to Seki and resided there," carrying the Sōshū-den manner east. Beneath that inheritance lay a Yamato foundation, legible in the descent of the Seki Zensada line through Kaneyoshi, so that the - the Seki workshops forged stands as a fusion of Yamato grain and activity in . From this founding the name multiplied across the period into , the last and largest body of the tradition; its representative masters at the close of the old-sword age were Magoroku Kanemoto, famed for the , and Izumi no Kami Kanesada, the smith called , while the Kanefusa, Ujifusa and Daidō hands worked beside them and the move of Wakasa no Kami Ujifusa to Kiyosu carried the body to the threshold of Owari .
A common vocabulary binds the Seki body, however widely its members range. The forging is an that stands and runs to , often mixed with and , over which rises the cool whitish of steel rather than the bright of ; this pale, standing is the constant tell the judges read first, present alike on Kinju's , Kaneyoshi's Ōei and 's late- blades. Over it the smiths temper into which the pointed of enters, with clinging to a tight , and , and streaming through; the answers in turning to a pointed or jizō-cast swept with . From this shared grammar the individual hands diverge. Kanemoto fixed the regular three-cedar of pointed teeth; Kanefusa devised the rounded-head, constricted-waist "Kanefusa "; Kinju and the early founders held a calmer, rounder away from the restless line, their work laid with thicker and dry, standing grain. The late masters carried the manner to a higher finish: wove among rounder forms for a broader temper than Kanemoto's one-sided file, and turned at times to a slender -styled with a hidden ; Kaneyoshi held instead to a cool , the disciplined Yamato face of late Seki, lightly broken with .
A collector seeks Seki because it is the connoisseur's ground for reading - across a vast body of signed and attributed work. The runs through the first: the standing, -leaning and the whitish separate a Seki blade from and Yamashiro, after which the pointed , the dry , and the pointed or jizō confirm the province; the discriminations the judges draw, Kinju held apart from by his rounder , parted from Kanemoto by his breadth, give the eye its anchors. Within the school the standing of the best members is settled: Magoroku Kanemoto for the , whom the swordbooks call simply "an excellent master" and the most accomplished of the several Kanesada hands, and the early Kinju as a rare and precious founding name, his record running through the tier with the signed pieces few and the long blades attributed . Signature works carry real provenance: a Kinju presented to the Tokugawa shogunal house in 1679, a borne by a chief retainer of the Tokugawa and a forged for the father of Takeda Shingen, a Kaneyoshi transmitted in the Kuroda family. Beyond connoisseurship, Seki's blades earned a battlefield reputation for cutting; the full and stout build of the , made to sever, set the standing that made the working sword of its age.