Nagasada signed himself Okatsuyama-roku Fujiwara Nagasada and gave his personal name as Matsui Jiichiro. He was born in Bunka 6, the year 1809, in Fuwa District of Province, the son of Matsui Naosaburo, and the published record traces a working life that moved across three provinces: for a time he served the Tokugawa house of Kishu as an official smith, around Man'en 1 he forged at Tamaru in , and from about Bunkyu 2 he settled at Aoyama in , where he made swords until his death in Meiji 2 at the age of sixty. The place-name Okatsuyama that recurs in his signatures refers to a locality north of Omotesa in his native district, the place from which he took his swordsmith's name. His dated blades fall within the closing years of the period, a of Keio 1 finely forged at among them, and they place him squarely in the revival rather than in the of the old tradition from which his school name descends.
His characteristic hand is a bold, broad-bladed built to the heroic proportions the late- smiths favoured: a wide carrying little taper from base to tip, a thick , a shallow , and an extended , the whole given a stout and magnificent bearing. Set over this construction is a flamboyant into which large , round-headed , small and occasionally pointed elements are mixed. The published sources describe the pattern as華やかに乱れ, a brilliantly animated , with and entering vigorously, the deep and the adhering well and evenly, some of it coarser; over and through the temper run frequent , and long , and the is bright. One feature is so constant across his recorded work that the judges single it out: the back, a three-surface ridge that one of the published commentaries names as この工の見どころ, the point of interest particular to this smith.
The beneath that temper is a close , drawn tight and at times mixed with and , over which the lies thick and fine enter; on the longest of the recorded blades the grain stands a little open toward the , but the prevailing impression is of a dense, well-forged . There is no here, as there would be in a or Yamashiro ; the brightness of his work comes instead from the depth of the and the evenness of the . The answers the temper below it, running straight or with a shallow and turning back in , the very tip swept into , and on occasion tempered deeply through the with a returning ; one blade shows and where the hardening spills onto the back near the . The is on every example, finished with a and file marks dressed with , and carries the long signature that gives his full style and, on the reverse, the date and the place of forging.
The corpus that survives in the designated record is uniform in manner, all of it signed of his maturity, so that his work is read less through phases than through one perfected idiom seen at full strength. Within it the judges draw a register of intensity: the most brilliant pieces, those they call出色 and華やかな, press the large and round-headed and the deep to their flamboyant extreme, while quieter examples hold the elements in a tighter . The on two of the blades, the characters cut on one and on a , belong to the votive and martial taste that runs through bakumatsu work. The governing question the published sources return to is not of date or generation but of resemblance, for his manner sits so close to one famous neighbour that the eye must be told how to part them.
That neighbour is the Kiyomaro school. Repeatedly the commentaries state that his bold , his -deep and his profuse and could be mistaken at a glance for Kiyomaro's line, 清麿一門に見紛う in the recurring phrase. The distinction the judges then draw is exact, and it is the heart of his . Within the one does not find the -tinged elements or the angular that the Kiyomaro group habitually shows, 丁子がかった刃や角ばる互の目などは見られず; in their place the large and the round-headed stand out, occasional pointed teeth enter, and the turns back with a rounded tip rather than running pointed. By those features, together with the frequent , the published sources separate his hand from the lineage it most resembles. He stands, then, as an independent bakumatsu master who carried the Kiyomaro manner without belonging to it, a -born smith working the revival idiom for the Kishu Tokugawa and then in .
Nagasada is an uncommon name on the designated record. Five of his are held at , all of them signed, and none has been raised to a higher designation; provenance is recorded for one, which passed through the hands of Sato Yoshitoi. These are the blades a private collector might realistically hope to encounter, and they reach the market only from time to time and with patience, a designated of his appearing as a notable event rather than a regular offering. The judges' own summations give the measure of why they are sought: of the Keio 1 made for Nishibori Mitsunori, the published record says the workmanship in both and is exceptionally fine and the piece may be termed 代表作と称すべき, a representative work of the smith; of another it notes that the deep , the evenly adhering and the bright are especially worthy of remark; and of the most robust it observes that the large-scale bearing and the flamboyant temper together convey a powerful presence. A signed by Nagasada offers, in a single late hand, the heroic and the -laden Kiyomaro-school manner held just short of Kiyomaro himself.