Masatsune is a smith of , working from the end of the period into the early , and the published sources name him the representative smith of the Senoo line. Following the Genki Mekiki-sho and the Kokon Meizukushi, they divide the old swordsmiths of into the smiths, who as a rule sign with the character Tsugu, and the Senoo smiths, who descend from Noritaka and forged at Senoo, east of toward . Among the Senoo hands (Koreshige, Yasuie, Hirotsune, Tsunemasa, Moritsune, Yukimasa) Masatsune alone survives in some number: his examples "are not few, while extant works by the other smiths are rare". The enters the first-generation Masatsune in the 'ei era, yet extant blades descend no later than the early , and the sources add that more than one smith seems to have used the name, with a range of signing manners.
His recognized blade is the slender of classical, graceful shape, high in with pronounced , several still signed with the two-character . The temper is a quiet one: a or narrow base into which and small enter, with and well inside, well attached, and fine and in places. The is at times tight, but the published sources state the usual case plainly: "in most, compared with , the is somewhat subdued and the grain stands". The runs straight and turns back in a small , now and then narrowing toward a -like finish. Read against the Masatsune it resembles, his work is called "somewhat plainer, with an astringent, subdued taste".
The carries the character. He forges a , well packed on the finest blades, standing a little in places and mixed with , with and fine . Through it run the speckled that the sources call , at times with clear , and a -style or quiet irregular rises. The tang is filed in , and the sources state that on the Masatsune the filing is always . These three points, the crepe-like , the in the forging and the original filing, are the ones the newer designations name again and again as the marks of the Senoo Masatsune.
The resemblance to runs close enough that the sources concede that "among them are works almost indistinguishable from ". Several show how the question is settled: each looks at first sight close to Masatsune and is re-read on the evidence of its and original filing. One of them carried an by Kōyū of the Genbun era for the Masatsune, and at its designation the sources conclude that it "is properly judged the Senoo Masatsune". The signature, too, is placed on either face, the or the , where the Senoo smiths otherwise favour the . Beside the signed stand the attributed to him, judged by the same , quiet and turnback. The dating the sources leave open: because the name passed through several hands and extant works run earlier than the 's 'ei date, one signed was designated as a blade merely bearing the signature, the question deferred to future study.
Within the Senoo line he is its representative and the one whose hand is most often read. The published sources call his work "archaic and deeply flavored", preserving the refined bearing of the transition from late to early , and on one signed judge it "the most archaic in character among works of this name". Of a later they write that it is "a truly archaic blade, with a moist quality in the and , and of high dignity", and they name a at Tsurugaoka Hachimangū as the typical work of the smith.
His record is fuller than the old view of a rare name allows. Twenty of his blades stand in the and tiers, four of them , of which two are called especially well made among his works; three more were designated before the war, one signed , which the entry judges as tradition holds, is recorded in Honma's inventory of the Imperial collection, and the Tsurugaoka Hachimangū , dedicated to the shrine by the shogun Tokugawa Yoshimune, is a National Treasure. Six further signed , their plates dating them to the period, are Important Cultural Properties, held among others by the Kumano Hayatama Taisha, the Takisan Tōshōgū and the Shirotori Jinja. Several retain their original tang and signature, which the sources call "especially valuable for remaining and signed", and one they name "one representative work of Masatsune". One was formerly held by the Arisugawa-no-miya princely family, and a survives in an early-Meiji mounting with fittings by Fuchikawa Kazunori. Most of these blades are held rather than traded, and a signed Senoo Masatsune comes to market only seldom; a privately held example remains a notable thing for a collector to encounter.