Kuwana, in Province, gave the Sengo line its base, and from there the Muramasa (村正) name carried the work of late- into the Sengoku decades. The oldest extant date in the whole line is Bunki 1 (1501), carried by a signed "Seshu Kuwana-ju Uemon-no-jo Fujiwara Muramasa "; from that anchor the prevailing scheme reads the Bunki pieces as the first generation, the Tenbun as the second, and the Tensho as the third, with the second master held the most skillful and most prolific of the three. The published sources set aside the popular tale that the founder studied under Masamune, calling it an unfounded tradition; the line begins instead near the close of the period. Its hand shares common features with , Shimada, and Sue-, and resembles Heianjo Nagayoshi of Kyoto so closely that the judges presume some relationship between the two, while a likeness to the Shimada smiths and to the Kanesada is noted as a thing that can confuse a first reading. From the workshop issued the disciples Masashige (正重) and Masazane (正眞), filed by tradition as students of the , who carried the manner forward alongside the Muramasa name itself.
The feature the commentary names again and again as the school's own is the matched temper: the on and align to one mirror-image pattern (- soroi), and the valleys of the press in toward the cutting edge. To this the masters add box-shaped elements (-), a and base mixed with compound , , and figures, the drawn tight with patchy in mura, and running frequently; the runs or to a , often swept with . The forms that carry it are the wide and with , and the short, strongly -zori ; the is tending to stand, mixed with flowing and -inclined grain, the steel dark at times and showing the whitish cast the descriptions repeatedly note. Beneath sits the , the fish-belly swelling that grows pronounced from the second generation, cut with a thick-chisel two-character . The successors diverge by proportion rather than trick: Masashige opens the vocabulary out, his grain standing more openly and his and carried further; Masazane draws it in, holding box teeth low at the under a calm , his closing tighter than his fellow pupil's. Beside the flamboyant rule each smith keeps a quiet register, in aimed at the manner, and an occasional reach toward with and , never the rule of the work.
To the school, the matched faces are the first tell: the aligned and , the box figures, the valleys pressing to the edge, the tight with its patchy , and the under the thick part Muramasa from the , Shimada, and Heianjo hands it otherwise resembles. Within the line the decides: cut angular on Muramasa, it rounds out fleshily on Masashige, while Masazane is told from Masashige by his tighter steel. The Sengo reputation for cutting sharpness, with the valleys driven toward the , drew the Tokugawa legend that the blades brought calamity on the house; the sources handle it as recorded fact, noting that from the period many signatures were effaced for fear of the name, so that signed in particular grew comparatively rare, and that one of Masazane's was cut "Yamashiro Province Masazane" as a deliberate screen for a recipient. Provenance runs through private and hands rather than institutional holdings: a first-generation transmitted as a possession of Oda Nobunaga, a Masazane descended in the Mizuno and Tosa Yamauchi houses, a Lotus Sutra held in the Nabeshima line. The Nichiren devotion read off some blades, the title Myoho--kyo cut into the steel, ties the work to its region. A signed, Sengo blade of secure date and matched temper comes to notice only from time to time, the legend that thinned the signatures adding to the call for those that remain.