Masatsune (正恒) is a representative swordsmith of the Senoo line of Province, a lineage tracing its origin to Noritaka (則高) and distinct from the mainstream. As classical sources such as the Genki Mekiki-sho and the Kokon Meizukushi observe, the smiths customarily employ the character "tsugu" (次) in their signatures, whereas the Senoo smiths — including Masatsune, Koreshige, Yasuie, and Hirotsune — do not. The Senoo forging area lies in the lower basin of the Takahashi River, positioned east of and closer to , a geographic circumstance that appears to bear directly upon stylistic affinities. It does not appear that "Masatsune" was confined to a single individual; various signature styles are observed among pieces bearing this name, and the repeatedly notes what may have been "some connection" with the contemporaneous Masatsune — a question that "remains a subject requiring further investigation." Surviving works are not especially few, and the smith is consistently regarded as the foremost representative of the Senoo group.
In workmanship, Senoo Masatsune closely approaches production of the period, to the degree that even Koyu once issued an attributing a Senoo blade to Masatsune. The is characteristically a dense (小板目) mixed with (杢目), upon which fine (地沸) adheres and delicate (地景) enter; or appears faintly. The is fundamentally (直刃) with shallow (湾れ), mixed with , , and ; and enter well; adheres; (金筋) and (砂流し) run throughout. The frequently shows an — a moist, subdued tendency — that constitutes one hallmark of differentiation from . Critical diagnostic features include the taking on a crepe-like texture () with or emerging, and the running in — features that, as the consistently state, "disclose the salient traits of workmanship." The typically runs straight in , sometimes with .
The evaluations return to a consistent cluster of phrases: blades whose and are — "sound and well-preserved" — and whose workmanship is "particularly superior" or "especially fine" among the smith's oeuvre. Old transmission texts describe the Senoo manner as "resembling work" (-mono ni nitari), yet the examiners are careful to identify features that reveal "an individuality characteristic of work" beneath the superficial resemblance. Signed examples are prized as valuable documentary material, and the of the best pieces is said to convey and "an unmistakably archaic tone, giving the blade a high degree of dignity." Within the broader tradition, Masatsune occupies a position of particular importance: a smith whose finest works approach — and by some accounts rival — the quality of , while retaining the distinct identity of the Senoo school.