Kagemasa of , who styled himself Shinshi Saburō, is a mainline smith of the late 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 he made jointly with Kagemitsu bearing dates of the Shōchū and Karyaku eras, one of them an Imperial and one designated . 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". His latest date, Ryakuō 3 (1340), carries his hand into the earliest generation of .
His characteristic hand is Kagemitsu's manner brought one half-step short of Kagemitsu's order. Over a finely forged he tempers a built on angular and -style , mixed with , small and a little , the whole inclining in , the reverse-slant of the late mainline. and enter the , fine and run through it, and the is bright with . On the signed in the published sources gather these features into a single judgment, that "in both and the distinctive traits of Kagemasa are well expressed". The 68th 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" and in "a somewhat stronger degree of variation within the , which is where Kagemasa's points of interest emerge".
The is the proper mainline steel and the firmest part of his identity. The forging is a closely packed , at times mixed with or running a little toward and ; very fine lies on it thickly, fine enter, and over this stands a vivid , which the sources call the bright, well-refined steel of a "finely wrought forging in the manner of the mainline ". The answers the : a or turning in , and on the dated and 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 is the constant that holds across signed and unsigned alike.
The corpus draws two registers and a temporal arc. On the and core prevails; on and he turns instead to a quiet . The Jūyō-Bijutsuhin of Karyaku 2 (1327) shows an orderly in that, set against Kagemitsu, is "larger, opening at the base, mixed with a tendency", and carries a sankō-tsuka-ken and among its Buddhist carvings; his signed runs a narrow with , and a -like . Across the period the dated move from Bunpō through Ryakuō 3, the latest reaching the first years, and the published sources read a deliberate restraint into them: on more than one blade the "shows a slight , a subtly subdued tendency, and this too marks a point of interest in Kagemasa".
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 , its signature cut away below the character Kage, is judged beyond doubt his because the workmanship "rivals Kagemitsu". It is exactly this small shortfall that does the appraising: a blade that reads like Kagemitsu but stops a touch short of his finish is given to Kagemasa, and most of his surviving work is attributed on that reasoning, eleven signed pieces against eleven unsigned in the official record. He worked, the sources note, in the and that were Kagemitsu's own specialties, which is why the two are so hard to part and why his bright and the slightly freer play of his are made to carry the distinction.
Fujishiro grades him Jō-jō . Twenty designated works stand on the official record, four in the tier and sixteen , with the Jūyō-Bijutsuhin above them; signed examples are so few that each is treated as study material, the published sources valuing one , single- dated Ryakuō 3 as "excellent material for research on this smith" and his rare signed as a piece prized "for understanding the workmanship of a smith whose signed pieces are scarce", one "filled with archaic grace and refined dignity". Provenance is recorded against three of his blades, among them the once held by Ide Hiroshi of Tokyo and a transmitted in the Sakai family of Wakasa; one signed 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 names are, his blades sitting in the and 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, is a landmark when it does.