Kagemasa of Osafune, who styled himself Shinshi Saburō, is a mainline Bizen smith of the late Kamakura period whose place in the school is fixed less by his pedigree than by his company. The published sources are candid that his genealogy is not clearly known, telling him variously as Kagemitsu's pupil or his younger brother; what settles the matter is a collaborative tachi he made jointly with Kagemitsu bearing dates of the Shōchū and Karyaku eras, one of them an Imperial gyobutsu and one designated kokuhō. From those joint pieces he is read as a smith who stood in extremely close relation to Kagemitsu, and the surviving dated works run across Bunpō, Shōchū, Karyaku and Kenmu, so that the Jūyō-Bijutsuhin commentary can say plainly that he was "clearly a disciple within the Kagemitsu line"[[c:1]]. His latest date, Ryakuō 3 (1340), carries his hand into the earliest Nanbokuchō generation of Osafune.
His characteristic hand is Kagemitsu's manner brought one half-step short of Kagemitsu's order. Over a finely forged ko-itame he tempers a midare built on angular kaku-gunome and kataochi-style gunome, mixed with ko-gunome, small togariba and a little ko-chōji, the whole inclining in saka-gakari, the reverse-slant of the late Osafune mainline. Ashi and yō enter the ha, fine kinsuji and sunagashi run through it, and the nioiguchi is bright with ko-nie. On the Tokubetsu-Jūyō tachi signed in orikaeshi-mei the published sources gather these features into a single judgment, that "in both ji and ha the distinctive traits of Kagemasa are well expressed"[[c:2]]. The 68th Jūyō tachi sharpens it further, finding his own points of interest precisely where he departs from his model, in that he "mixes an even greater variety of tempering forms than Kagemitsu"[[c:3]] and in "a somewhat stronger degree of variation within the midare, which is where Kagemasa's points of interest emerge"[[c:4]].
The jigane is the proper mainline Osafune steel and the firmest part of his identity. The forging is a closely packed ko-itame, at times mixed with mokume or running a little toward nagare and masame; very fine ji-nie lies on it thickly, fine chikei enter, and over this stands a vivid midare-utsuri, which the sources call the bright, well-refined steel of a "finely wrought forging in the manner of the mainline Osafune"[[c:5]]. The bōshi answers the ha: a midare-komi or notare-komi turning in ko-maru, and on the dated and ubu tachi it takes the sansaku-like form the school shares, so that the cap too "calls Kagemitsu to mind." The steel can tend slightly dark, and the utsuri is the constant that holds across signed and unsigned alike.
The corpus draws two registers and a temporal arc. On tachi the kaku and kataochi-gunome core prevails; on tantō and ken he turns instead to a quiet suguha. The Jūyō-Bijutsuhin tantō of Karyaku 2 (1327) shows an orderly gunome in ko-nie that, set against Kagemitsu, is "larger, opening at the base, mixed with a kataochi tendency"[[c:6]], and carries a sankō-tsuka-ken and gomabashi among its Buddhist carvings; his signed ken runs a narrow hoso-suguha with kinsuji, sunagashi and a nijūba-like yubashiri. Across the period the dated tachi move from Bunpō through Ryakuō 3, the latest reaching the first Nanbokuchō years, and the published sources read a deliberate restraint into them: on more than one blade the ha "shows a slight kozumi-gokoro, a subtly subdued tendency, and this too marks a point of interest in Kagemasa"[[c:7]].
His standing in the school is defined against Kagemitsu at every turn, and the comparison is the whole of the connoisseurship. The published sources are consistent that in rank he yields a little to Kagemitsu while in style he stands very close, skillful and faithful; the 4th Tokubetsu-Jūyō tachi, its signature cut away below the character Kage, is judged beyond doubt his because the workmanship "rivals Kagemitsu"[[c:8]]. It is exactly this small shortfall that does the appraising: a mumei blade that reads like Kagemitsu but stops a touch short of his finish is given to Kagemasa, and most of his surviving work is mumei attributed on that reasoning, eleven signed pieces against eleven unsigned in the official record. He worked, the sources note, in the kataochi-gunome and suguha that were Kagemitsu's own specialties, which is why the two are so hard to part and why his bright midare-utsuri and the slightly freer play of his midare are made to carry the distinction.
Fujishiro grades him Jō-jō saku. Twenty designated works stand on the official record, four in the Tokubetsu-Jūyō tier and sixteen Jūyō, with the Jūyō-Bijutsuhin tantō above them; signed examples are so few that each is treated as study material, the published sources valuing one ubu, single-mekugi-ana tachi dated Ryakuō 3 as "excellent material for research on this smith" and his rare signed ken as a piece prized "for understanding the workmanship of a smith whose signed pieces are scarce"[[c:9]], one "filled with archaic grace and refined dignity"[[c:10]]. Provenance is recorded against three of his blades, among them the tantō once held by Ide Hiroshi of Tokyo and a tachi transmitted in the Sakai family of Wakasa; one signed tachi is now in the Hakutsuru Museum, the rest held in private hands of recorded whereabouts. A Kagemasa is not beyond a collector's reach as the most exalted Osafune names are, his blades sitting in the Tokubetsu-Jūyō and Jūyō tiers rather than held in perpetuity in the museum and shrine collections that hold the school's highest designations; but with so small a signed corpus and so few coming to market, an example appears only from time to time, and a signed, dated, ubu tachi is a landmark when it does.
