A tachi signed Bishū Osafune Sukemitsu and dated the eighth month of Eikyō 9 (1437) is the earliest dated work of this Osafune smith, and the published sources call it an ubu, signed tachi in the manner known as Oei-Bizen, "an imposing work"[[c:1]]. His dated blades continue through Kakitsu, Bun'an, Hōtoku, Kōshō and Kanshō, and a wakizashi of Bunmei 5 (1473) carries the name further. The Meikan lists seven smiths signing Sukemitsu, and the NBTHK takes this one, judging from his dates, as the first among them. On several blades he adds the common-name title Rokurōzaemon no Jō, and those pieces identify him as the father of the brothers Ukyō no Suke Katsumitsu and Sakyō no Jō Munemitsu. The proof is a Munemitsu tanto dated Bunmei 9 signed "Osafune Sukemitsu's second son, Sakyō no Jō Munemitsu"[[c:2]], a blade the published sources say shows well the transition from Oei-Bizen into Sue-Bizen.
His characteristic temper is a gunome that opens wide at the waist, the koshi no hiraita gunome, mixed with a little chōji, nioi-dominant with ko-nie, with fine kinsuji and sunagashi running within and a bright nioiguchi. On the Eikyō tachi it is mixed with pointed elements; on a Bun'an 5 tachi it carries pointed and angular teeth and in places recalls shima-ba. The published sources describe that Bun'an tachi as full in its contours and healthy, a fine piece that "fully displays the height of his skill"[[c:3]]. It carries on the ura a gold-inlaid cutting-test inscription of Manji 1 by the tester Yamano Kaemon no Jō Nagahisa.
The jigane is an itame mixed with mokume, at times flowing or standing, with ji-nie and well-entered chikei, and over it a bō-utsuri stands, faint on some blades and clear on others. The bōshi runs in a midare-komi to a ko-maru, or runs straight and points as it turns. A Bun'an 6 tanto with slight uchizori shows the whole manner on a small scale: a standing itame with mokume, thick ji-nie, chikei and bō-utsuri, under a waist-open gunome and gunome-notare with abundant ashi and a little yubashiri. The published sources call it a superb piece "showing Sukemitsu's typical manner, its merits displayed throughout"[[c:4]]. It is incised with the deity name Ichinomiya Daimyōjin.
The published sources read his dated work as a single hand crossing from Oei-Bizen into Sue-Bizen. Of a Kakitsu 3 wakizashi they write that the construction and the ji and ha still show an Oei-Bizen flavour, but that "the smaller amplitude of the midare and the inconspicuous chōji show that the date has descended"[[c:5]]. A Kōshō 3 tachi keeps the high koshizori of a tachi with a waist-open gunome mixed with chōji, while a Kanshō 3 katana, signed in full with the Rokurōzaemon title and fitted with a brocade-wrapped handachi mounting, has a suguha-toned temper with gunome ashi and a tightening nioiguchi above. Of it the published sources write that "works with this signature are very few, its carving fine, and it is well made as Sue-Bizen"[[c:6]]. His carving is notable throughout: kurikara, bonji and sutra text, twin grooves, and sacred names.
He also tempered a chū-suguha. A wakizashi of Hōtoku 3 is inscribed on the ura as made at Takehara in Settsu, a record of the period when Bizen smiths moved to work in other provinces, as Katsumitsu did in Bitchū, Kojima, Kyoto and Ōmi. The published sources call it "not only good material for the study of the Sue-Bizen smiths but a fine work in chū-suguha"[[c:7]]. The Bunmei 5 wakizashi, recorded in Honma's inventory of the Imperial collection, is of the same quiet kind: an itame flowing slightly and standing, with a whitish bō-utsuri, under a chū-suguha with a slight notare and ko-nie, carved with bonji and a sankoken over twin grooves and inscribed with the deity name Tenshō Daijingū. Honma gives the Meikan's scheme of five generations of the name but adds that "whether this division is correct must await further study"[[c:8]]. He finds the smiths of the name "skilled in both suguha and midare"[[c:9]], and calls the Tenshō Daijingū inscription "worth noting together with the Ise faith"[[c:10]].
For the collector, Sukemitsu's record is seven blades designated Jūyō, every one signed and dated on an ubu tang, with no blade in the higher tiers. No provenance is recorded for them. The published sources stress how few works carry his full Rokurōzaemon signature, and a dated, carved blade from the head of the family that led Osafune into the late Muromachi appears only from time to time; it is valued as a document of the passage from Oei-Bizen to Sue-Bizen.