Kunimitsu (新藤五国光) of Province was, in the words of the , "in effect, the founder of -." Active during the late period, his earliest extant dated work bears the inscription "Einin 1 (1293), tenth month, third day" with the long signature "-junin Kunimitsu ." Old transmitted records state that Kunimitsu had three sons — Kunishige, Kunihiro, and Kunitai (or Kuniyasu) — who later also signed under the name "Kunimitsu," a circumstance confirmed by the variety of signature styles observed among extant works and by dated inscriptions spanning from Einin 1 (1293) through Gentoku 3 (1331). His paramount achievement, as repeatedly emphasized across designation records, is that "he fostered three great masters among his disciples — Yukimitsu, Masamune, and Norishige," an accomplishment described as being "of the highest order." As a master of the , he is consistently ranked alongside Toshiro Yoshimitsu as forming the "twin peaks" of the genre.
Kunimitsu's style, "at first glance, can call to mind works of the school"; however, the identifies him by "the conspicuous and manifested in both and ." His forging characteristically shows closely packed or mixed with and , upon which thick adheres densely and enters with great frequency; often stands out. He "excelled particularly in , producing many variations — threadlike, fine, medium, and broad ." His typically presents a or with deep , well-adhering , and a that is consistently described as "bright and clear." Within the tempered edge, appear "in profusion" — likened in one celebrated description to "an old man's whiskers" (okina no hige) — accompanied by running and fine along the . The is straight, turning back in , sometimes with . Surviving are exceedingly rare, with most extant works being ; the few long swords display an elegant silhouette with high , , and , while retaining the dense and active found in his short blades.
Across the designation literature, Kunimitsu's works are praised for steel of exceptional clarity — described as "powerfully clear and bright" — and for a of "outstanding level of workmanship." The recurring evaluative language emphasizes that his finest pieces display Kunimitsu's "distinctive character brought forth to its fullest extent," with and that are (sound and well-preserved), "without the slightest slackness." His building upon an -derived tradition, advancing it by "laying more thickly across both and and giving pronounced expression to activities such as and ," is understood as the foundational step that enabled the subsequent flowering of the tradition under his students. Works bearing dated inscriptions, particularly those of the Enkyo and Genkyo eras, are singled out for "high documentary importance." Several pieces carry distinguished provenance through the Uesugi, Date, Matsudaira, and Satake families, and one is recorded in the addendum of the Kyoho -cho as "though not a , a fine implement."