Masatsune (正恒) stands alongside Tomonari as one of the twin pillars of the school, active in Province from the late period through the early period. It has long been transmitted that there were three generations — or possibly more — bearing the name, and their collective output spans a considerable arc of time. Among the smiths, Masatsune has left the greatest number of extant signed works, and it is especially noteworthy that across this body of work "their workmanship shows no unevenness in quality." In the neighboring province of , the school also includes a smith of the name whose manner of workmanship is similar. Masatsune's signatures are invariably cut in two characters, rendered with a thick chisel in a bold hand — a consistent trait that distinguishes his inscriptions from Tomonari's occasionally longer signatures.
The repeatedly position Masatsune against Tomonari in a complementary assessment: whereas Tomonari "is considered superior in the elegance of form — exhibiting a graceful, feminine refinement," Masatsune "is judged to surpass him in the intricacy and excellence of the ." His forging, typically a well-packed (小板目肌) or mixed with (杢目), produces abundant (地沸) with finely entering (地景). His — whether , , or madara- — "rises with striking clarity," a hallmark that appears "comparatively clearly" in his work where it is "not especially conspicuous" in Tomonari's. The (刃文) is characteristically -based (直刃調), mixing , , and , with plentiful and ; thick (小沸) adheres well, and (金筋) and (砂流し) appear frequently, producing a that is consistently described as "bright and clear." The typically proceeds straight and turns back in , often with at the tip — a pattern noted as characteristic of this smith. The more flamboyant examples display standing out prominently, and appearing in dotted succession, and intermittent -like effects that reveal "an even stronger rustic flavor."
The evaluative language across Masatsune's designations converges on a distinctive aesthetic judgment: his works possess "an archaic yet highly dignified workmanship" that "clearly manifests the special characteristics of swords." The consistently praises the brightness and clarity of both and , and the condition of his blades is frequently extolled as (健全) — sound and well-preserved. Where Tomonari is credited with greater archaic flavor in the , Masatsune is recognized for "a refined taste" and works that are "more urbane and polished." His finest pieces are praised as displaying "a brilliance and clarity throughout both and " and as exhaustively manifesting "the high level of technique and the aesthetic virtues of " in forging and tempering alike. It is this combination — the supreme quality of the iron, the luminous clarity of the temper, and the dignified antiquity of manner — that secures Masatsune's position as one of the foremost masters of the tradition.