Muramasa was a swordsmith who resided at Kuwana in Province, representative of that province in the late period. Among extant works, the earliest dated example bears the year Bunki 1 (1501), regarded as the first generation; works dated to the Eishō and Tenbun eras are attributed to the second generation, and those of the Tenshō era to the third. Of these, the second generation is consistently identified in assessments as "the most skillful among the successive generations," with the greatest number of surviving works and the highest proportion of fine pieces. The popular tradition linking Muramasa to Masamune as a pupil is, as the plainly state, "an unfounded tradition." Certain stylistic affinities with Heianjō Nagayoshi and Izumi no Kami Kanesada suggest some form of relationship, though its precise nature remains unclear. The lineage is said to have died out after the Tenshō generation, "perhaps because the name became an object of avoidance by the Tokugawa shogunal house."
The defining hallmark of Muramasa's workmanship is the conspicuous correspondence of the on both and -- a matching temper that the regards as the principal diagnostic feature. The tempering is characteristically "box-like" (), with the valleys of the pressing close to the cutting edge and a that tends toward a tightly drawn appearance (). Within this framework, the range of expression is remarkably broad: the standard mode is mixed with , incorporating compound () , , and -like elements, all in with running through the temper. Yet examples in -like manner -- with , , and vigorous -- are "not infrequently seen," and one piece even "aims at the manner of the school and does so successfully." The is typically tending toward with and a somewhat whitish () cast, though the finest works achieve a dense with notably clear steel. Spears are also "accomplished and not especially few in number," with one monumental ōmi- of exceptional size praised as having been "forged so adroitly, without conspicuous coarse irregularity" that it would likely be "the outstanding example among works of this type."
Across more than fifty years of deliberations, the evaluative language returns to the constellation of virtues: both and are -- sound and well-preserved -- and the finest examples are those in which the and are "notably clear" (), the is "bright," and the workmanship is "excellent." The second generation in particular is praised for producing "a greater number of pieces of superior workmanship" than the first, and individual blades are singled out as being "especially superior" even within that elevated standard. The breadth of Muramasa's working range, from severe to flamboyant , combined with the unerring bilateral symmetry of the temper and the consistently tight , secures his position as the preeminent smith of Province and among the most distinctive voices of the late period.
