A tantō dated the fifth month of Shōhei 5 (1350) anchors the career of Nagamori of Bizen Osafune. Of his Shōhei-dated work the published sources write that it "raises the previous upper limit of his dates, and is valuable material for the study of Nagamori"[[c:1]]. Nagamori has been transmitted since old times as a son or pupil of Chōgi (Nagayoshi). His dated blades run from Shōhei 5 (1350) and Shōhei 8 (1353) through Shōhei 22 (1367) and the Kentoku years, to the lately surfaced Eiwa 4 (1378) and Kōō 1 (1389). They place him in almost the same years as Chōgi rather than a generation behind, and like his teacher he signed overwhelmingly with Southern Court era names. A Chōgi tantō dated Jōwa 6, the equivalent of Shōhei 5, is Chōgi's earliest dated piece, so the two stand together at the head of the dated record. One Tokubetsu Jūyō wakizashi goes further, noting that he "may even be seen as slightly earlier than Chōgi"[[c:2]].
His hand is Bizen work carried into the Sōshū manner of the Chōgi line. The temper is a gunome-midare whose waists open in the Chōgi manner, mixed with chōji, ko-gunome and angular, pointed elements, wide and varied in its line. Ashi and yō enter, ko-nie adheres, and fine yubashiri and tobiyaki are mixed through it. Kinsuji and sunagashi run in the ha, and the nioiguchi is bright and clear. The published sources grant the affinity with Chōgi in the opened waists and the variety of the temper, and then settle the attribution on one distinction: his midare resolves into somewhat smaller patterning than the teacher's. Of one blade they write that "in the way the midare becomes somewhat smaller in pattern, the attribution to Nagamori is convincing"[[c:3]]. They read this as a manner falling a little short of Chōgi and Kanenaga in vigour and technique.
He forges an itame mixed with mokume, the hada standing a little and flowing in places, with ji-nie laid on thickly in fine particles and chikei entering well. The published sources name the strong nie of ji and ha as the Sōshū-den character of the Chōgi line, and it gives his jigane its depth. A midare-utsuri stands over it, often only faintly, and the published commentary notes that among blades of this type "there are some on which no utsuri appears at all"[[c:4]]. The bōshi runs in midare and turns back in a ko-maru, at times rising to a pointed tip with hakikake; on the signed pieces it runs up and turns back long. Bō-hi is carved through on most of the shortened katana, and the signed tantō carry su-ken and gomabashi.
His record falls into two groups. The first is a small body of ubu signed and dated work, mostly tantō and short tachi or wakizashi, with a long signature on the omote and a date on the ura. Its peak is the Shōhei 16 wakizashi in the Tokubetsu Jūyō, a wide, elongated hira-zukuri tempered in a large gunome-midare with deep nioi and abundant nie, which the judges read as showing the Sōshū-den. They call it "one of the foremost among Nagamori's works"[[c:5]]. A Shōhei 21 tantō recorded in Honma's inventory of the Imperial collection belongs to the same group. Its entry observes that his signature is close to the Osafune work of the period and differs from Chōgi's, and that "surviving works are very few, and await further study"[[c:6]]. The second and far larger group is the ō-suriage mumei katana, wide in body with an extended or large kissaki in the Nanbokuchō shape, attributed to him by the smaller-patterned reading of the Chōgi style. The published sources stress that beside the opened gunome he leaves a varied small ko-gunome midare, shallow notare and even suguha-toned work, and they call him "a smith of comparatively broad range"[[c:7]]. That breadth, with so few signatures to set against it, is why the mumei attributions turn on so fine a point.
Within Nanbokuchō Osafune he belongs to the Chōgi group, beside Kanenaga and the other Sōshū-den hands of the school, and the comparison the judges draw most often is with Chōgi himself. His midare-utsuri and the brightness of ji and ha keep him a Bizen smith. The thick ji-nie, abundant chikei, kinsuji and sunagashi place him within the Sōshū manner of the Chōgi line, while the smaller scale of his midare and a slightly gentler force separate him from the master. One blade is praised for a bold and splendid air, its midare varied and showy and rich in activity, an excellent work convincingly attributed to him.
Fujishiro grades Nagamori Jō saku. He has no National Treasure and no Important Cultural Property. His record runs through one Tokubetsu Jūyō and thirty-nine Jūyō blades, forty across the two tiers, with the Shōhei 21 tantō recorded in Honma's inventory of the Imperial collection, forty-one works on record in all. Of recorded whereabouts, two are held by the Tokyo and Kyoto National Museums. A mumei katana of Jūyō rank carries a silver-inlaid ownership inscription of Fukushima Kamon-no-suke and an incised note by Tagaya Eishi, who wrote that he bought it with his stipend, wore it always, and bade his descendants keep it. Because authenticated signatures are extremely rare, the dated pieces are valued as evidence as much as objects. A signed Nagamori comes to market only seldom. The mumei katana attributed to him appear more readily, Chōgi-line Sōshū-den blades of bright steel and varied temper within the reach of a patient collector, and a documented signed example is a notable thing to encounter.
