In the tenth month of Einin 1 (1293), a blade left the forge of Kunimitsu bearing the long signature junin Kunimitsu , the oldest of his dated works. The published sources count Kunitsuna and the smiths Kunimune and Sukezane as the pioneers of sword-making, settlers from older centers; the first smith of itself, who cut his residence and his dates into the , was Kunimitsu. His designation texts open with one standing sentence for half a century: he is the de facto founder of the tradition, and the raising of the three masters Yukimitsu, Masamune and Norishige is counted his great achievement. Tradition makes him the son of Kunitsuna and a pupil of Saburo Kunimune, a transmission the sources say still leaves room for study. His dated work runs to Gentoku 3 (1331), and a of Showa 4 (1315) signed with the Buddhist name is read as late work, beside the dates of Kagen and Tokuji.
What survives is, before all else, the : and , of ordinary width with , and signed with the two-character . The sources state his formula in a single sentence: at a glance the work suggests , but the conspicuous and expressed in and point to this smith. He excels in across its whole range, , hoso, chu and hiro; as a master of the he is paired with Toshiro Yoshimitsu, the two named twin peaks (短刀の名手として藤四郎吉光と双璧). The temper is bright with small , crossed by fine that flicker; the appraisers have called this play the old man's whiskers (翁の髭) from of old and count it the great point of his work. Honma adds a habit of the hand: the temper ordinarily hardens down past the toward the ; a few authentic pieces instead drop the slightly there. The runs to a calm , at times lightly swept; , and are carved on many blades, and the construction recurs.
The is where his schooling shows. He forges a or a tightly knit , and lays over it thick and often , minutely fine; enter incessantly, the steel is clear, and frequently stands. The standing that came to mark the mature tradition is almost wholly absent in his own blades, and grows only by degrees in the men after him; the sources note it chiefly in his rare work, while the norm is a surface so refined it passes for until the and betray it. The of these quiet lines is singled out as well, the light-beautiful the texts call particular to the upper rank of work. From this refined, -laden his three pupils drew out the - of the mature tradition.
are another matter: the sources repeat that the are rare and nearly everything extant is ; the survivors are slender, with high , and a compact point, forged exactly as the . The signed that the sources assign by their signature to one of his sons, the Mutsu among them, are recorded under the later-generation Kunimitsu. The attributed to him belong here too, and the sources are explicit that such a judgment names Kunimitsu and his three sons collectively. One such blade carries a Kyoho 7 (1722) of Kochu at seventy gold pieces. A small minority departs from the norm altogether: a tempers its lower half in a large , the text stating plainly that his is scarce and this piece well made. Honma reads in that scarcity the proof of the school: exists, if rarely, in Kunimitsu, and , if most rarely, in Masamune, the two together confirming the relation of master and pupil. A single katakiriha , retempered, is the only one of its construction in his work.
The name ran on past the founder. The old registers give him three sons, Kunihiro, Kunishige and Kuniyasu, all said to have signed Kunimitsu later, and only Kunihiro is met with under his own name; since the hands cannot yet be divided by workmanship, the sources divide them by the . Three signed recorded in Honma's inventory of the Imperial collection carry unlike the Aizu , yet the entry finds no taint of a false signature in any of them and suggests that the sons may best be seen as - hands for their father. The founder's two-character signature follows the rule the appraisers call saji kitakanmuri (左字北冠), the interior of the character cut in the left-hand manner with the crown set toward the , in both a fine and a thicker chisel, and the texts admit rare authentic exceptions. On the sits on the toward the ; an signed of 96.1 cm is read as Kunihiro's Kunimitsu from its workmanship and deep, bold carving, and so belongs to Kunihiro. The carving is itself a legacy: the layered later seen in Sadamune is judged to begin with , and the work on his blades is connected with Daishinbo Yukei, transmitted as his pupil and a master of the chisel.
Much of this oeuvre is patrimony. Three blades hold the rank of National Treasure and ten more are Important Cultural Properties, preserved in museums, shrines and long-held collections; seven are prewar , among them of the Seikado and the Kurokawa Institute. The provenance roll runs deep. The -toshi passed from Toyotomi Hideyoshi's Osaka treasury through the fire of the summer siege, was retempered by the first Yasutsugu, and descended in the Tokugawa shogun house; his are handed down in the Uesugi of Yonezawa, the Matsudaira, the Satake, the Hosokawa and the Ogasawara, and one blade entered the collection of W. A. Compton in recent times. Fujishiro rates him Sai-jo , and sixty-nine designated works stand on record, the great majority signed, most often with the two-character in an , the long signature met only a few times. What a private collector may realistically encounter is the and tier, seven and thirty-nine blades, forty-six in the two tiers together, most of them signed of the classic refined manner. Such pieces are held closely and reach the market only rarely; when one does appear, it carries the signed work of the smith in whose forge the tradition began.