Sadatsugu worked in at the end of the and in the early period as one of the representative smiths of . The published sources explain that was known from early times as an iron-producing province, and that the smiths forged and flourished in the districts of Ko'i and Manju on the lower Takahashi River; the work of the school from the end of the to about the middle of the period is called . They name Sadatsugu with Moritsugu, Yasutsugu and Tsunetsugu as its representative smiths. Since the Kanchiin-bon Meizukushi he has been transmitted as one of the who served the cloistered sovereign Go-Toba In, and the same name was carried on down to the period. The commentary holds Sadatsugu to be known for a particularly high level of skill within the school, yet adds that his surviving works are extremely few, a handful that can be counted on the fingers.
His recognized hand is the slender in with . The two signed of the and tiers are both shortened, yet both keep a high and a compact . The published sources find an archaic dignity in that shape, and of the later of the two they write that the slender with its high is graceful and carries a sense of refinement. The National Treasure keeps the form uncut: its tang is , and it is a slender with a high , and a , inclining slightly forward toward the tip in what the published sources call a graceful shape.
The is the constant of his work, and is recorded on three of his four blades. On the two shortened it is a well-packed mixed with that stands a little into the crepe-like texture called , with adhering well, fine and patches of . The National Treasure is a well-packed with thick , and , and a faint ; its commentary names the . Of the , first designated in the tenth session, the published sources write that the shows the mark of the school. They describe work in general the same way: a in which the stands out, often mixed with , under a temper that is well formed in and, compared with contemporary work, somewhat plain and astringent in taste.
Over that the temper stays close to a base. On the National Treasure it is a -toned with small and and , rich in variation within the , the deep and bright, and the undulates slightly before turning back round. On the it is a mixing and , with and , a bright , and in places. The published sources call it comparatively florid for the school, yet showing the quality of its age. The later carries a with that rises and falls a little, and frequent and thick, spilling into the in places with , , and . On the earlier record of the the runs straight and turns back in a large-round on the and a small-round on the , with a little .
The tang carries the rest of the evidence. smiths cut the on the and finish the tang in large file marks, and the published sources note that the signature is a point of difference from . On the the two-character is fluent and cut with a fine chisel mixed with reverse strokes. The later is an exception, an exceptionally rare example in which Sadatsugu cut his signature on the obverse, authentic yet a little different in manner from his usual hand. The published record leaves open which of the several Sadatsugu was the earliest and the one meant by the tradition. It calls the , by both workmanship and signature, the most precious single blade for resolving that question. The National Treasure commentary, for its part, notes several smiths named Sadatsugu from the end of the to the period and identifies the maker of its as the Sadatsugu who served as .
Fujishiro ranks him Jō-jō . His record is crowned by a National Treasure , transmitted in the Sō family, lords of the Tsushima domain, and now in a private collection in Tokyo. Its commentary holds that it shows the features of well, the , the archaic and the signature, and that it is moreover of fine workmanship and well preserved. The compares the with the National Treasure Sadatsugu transmitted in the Sō Count family of Tsushima. He also has an Important Cultural Property with a gold-inlaid attribution and the name , its plate giving a mixed with and a mixed with . Only two of his blades stand in the and tiers. Of the later one the writes that, among the rare signed works of this smith, it is valuable also as reference material. Of recorded whereabouts, his blades include holdings in the Sano Art Museum and the Aomori City Museum. With so few signed pieces outside the national designations, a signed Sadatsugu comes to light only seldom, and a privately held example is among the rarer things a collector of early work could encounter.