A tanto signed Higo Daijo Fujiwara Sadakuni and dated Keicho 10 (1605) was designated Juyo at the sixtieth session; before it the published sources knew only a Keicho 14 (1609) tanto as his dated work, and they read his Keicho-shinto activity from it. He was a smith of the Echizen Shimosaka school, and the NBTHK places him as 「康継と最も密接な関係にあった下坂一門の刀工」 (the smith of the Shimosaka group in the closest relationship with Yasutsugu). That closeness was once read too literally. Edo-period sword books and registers scarcely record him, and the few that do treat him as the same man as Yasutsugu, helped by the likeness of their Higo Daijo signatures; today the two are understood as distinct smiths. He signs Higo Daijo Fujiwara Sadakuni, often with Echizen-ju on the reverse. Honma's inventory of the Imperial collection records a youthful signature, 「越前国下坂貞国」. A small wakizashi signed Higo Daijo Fujiwara Shimosaka with Echizen-ju is judged his early work, since in the first Keicho years three Echizen smiths, the later Yasutsugu, Sadakuni and Kanenori, signed Shimosaka with the Higo Daijo title.
His hand is above all a suguha hand. The published sources write that he 「直刃を得意として乱刃の作は殆んどなく」 (excelled at suguha and made almost no works in midareba), and that his work is 「直刃調のものが多く, 僅かにほつれ, 小足が入り, 地刃共に沸も穏やかな感がある」 (mostly suguha-toned, slightly frayed, with ko-ashi, the nie of ji and ha alike giving a gentle impression). Faint ko-notare and small ko-gunome mix into the line, the nie is small and quiet, and the nioiguchi sinks rather than glows, with thin sunagashi and an occasional kinsuji. The boshi runs straight to a small ko-maru with hakikake, at times drawn down long or a touch pointed. A katana in Honma's inventory widens the manner into a hiro-suguha tone undulating shallowly with ko-midare, the nioiguchi subdued throughout. Honma's entry sums him up the same way: nearly all his work is suguha-cho, with gunome on some tanto; tanto are many, katana few, and naginata rare.
The jigane is where the published sources separate him from Yasutsugu. Beside the master's work, they write, his shows 「黒ずんだ杢肌などは少なく, 概ね鍛えがつみ」 (little of the blackish mokume, the forging generally packed). It is an itame that runs and flows, mixed with mokume, the shinogi-ji leaning to masame, the grain standing somewhat under well-applied ji-nie. One description states plainly that 「板目が流れているものが常で」 (the itame usually flows). On his better blades the sources find the jigane tighter and more refined than ordinary Echizen work, and they name that refinement as the point of interest of this smith. On the Keicho 10 tanto the steel takes on a dark cast, yet its precision still shows that hallmark.
A few wakizashi break the suguha rule, and the published sources treat them as signs of his range. One, a wide, extended kata-kiriha-zukuri wakizashi, has a low ko-notare mixed with gunome over a refined ji, with ko-ashi, ko-nie and fine kinsuji and sunagashi. It is read as a work in which he 「古作の貞宗や信国に範をとった」 (took the old Sadamune and Nobukuni as his model), a piece of subdued flavour. Another departs entirely from his norm. On a wide, extended hira-zukuri wakizashi he tempers a broad choji-midare mixed with gunome, round-headed gunome and pointed teeth, the ashi long and frequent, the nie thick with coarse grains, sunagashi and nie-suji running strongly. The sources liken it to 「一派の中でも最も丁子の目立つ日向大掾貞次」 (Hyuga Daijo Sadatsugu, whose choji stands out above the rest of the school), and find it remarkable that a smith whose rule is a gentle suguha-cho should temper so brilliant a choji-midare. Both blades are called 「貞国会心の一口」 (a piece into which Sadakuni put his whole heart), and the second 「同作中抜群の出来映え」 (outstanding among his works). The rest of the group stays nearer home, with shallow notare and ko-gunome on the tanto.
Carving is the third strand of his work. His blades carry deep, strong Echizen-bori, 「越前彫独得のもの」 (of the kind peculiar to Echizen carving): a Fudo standing on a rock within a hitsu, a kurikara, gomabashi and suken. Of the rock-borne Fudo on his early Shimosaka-signed wakizashi the NBTHK writes that it is a typical Echizen carving and very probably his own hand. Honma's inventory adds a tanto carved with crane and tortoise, an auspicious subject, and a plum branch. Honma asks whether Sadakuni's plum and bamboo stand at the source of Echizen-bori, finds some basis for the tradition that he first carved the blades of the first Yasutsugu, and supposes that the two fell out and that Sadakuni ended his life in Echizen. His teachers and pupils are not recorded.
Fujishiro rates him Jo saku, and eleven designated works stand on record, all of them signed: nine Juyo and the tanto and katana recorded in Honma's inventory. He holds no designation above Juyo, and no provenance or holding institution is recorded against his blades. Several carry the full long signature in fine chisel strokes, and one katana bears a six-character mei without Fujiwara, which the published sources call unusual. One of the Juyo blades is a naginata, a form they say survives from his hand now and then but seldom with an ubu nakago. For a collector he is a careful and individual name rather than a famous one. Blades by him come to market only from time to time, a tanto or wakizashi at Juyo level, and a signed and dated example is the piece to wait for.