Nagamitsu was the son of Mitsutada, founder of the school of Province, and is regarded as the second-generation master. Together with his father, he ranks among the foremost smiths of the tradition. Active from the mid to late period, with dated works spanning from Bun'ei through Ka'gen, Nagamitsu left the greatest number of extant signed works of any -period swordsmith. The consistently observes that these works "show no unevenness in quality, demonstrating the fullness and consistency of his technical accomplishment." - and -period transmission texts posit the existence of a first and second generation, with signatures bearing the title Sakon Shogen traditionally assigned to a successor; however, the notes that "no clear differences can be discerned in the chiseled characters" between the supposed generations, and the more persuasive modern view holds that "Shogen Nagamitsu" represents works from his later to final years.
Broadly speaking, his style divides into two principal modes: robust constructions that carry on the manner of his father Mitsutada, paired with flamboyant dominated by brilliant ; and blades of standard or slender proportions featuring a comparatively calm workmanship in a -toned temper enlivened by -. The former mode, considered earlier in his career, produces exuberant structures in which mingles with , , angular elements, and the distinctive (toad-spawn clove) inherited from Mitsutada. A hallmark of these works is the compositional device of raising the temper high around the middle of the blade and suppressing it lower toward the , creating pronounced variation. His characteristically displays tightly forged covered with extremely fine , interwoven with minute , and enlivened by vivid . The typically presents a shallow turning back in — the so-called "Sansaku " associated with the three great masters. Throughout both modes, the is consistently described as bright and clear, the temper -dominant with , and the internal activity of , , , and abundant and conspicuous.
The repeatedly characterizes Nagamitsu's works as possessing exceptional clarity in both and , employing the term — bright, clear, keen — as a near-universal hallmark of his steel. His technique is praised for its remarkable breadth of expressive scope: from works so floridly irregular that they call Mitsutada directly to mind, to quiet compositions that at first glance resemble Sanenaga or Kagemitsu. The rare surviving reveal the nascent emergence of that his son Kagemitsu would later bring to full fruition, positioning Nagamitsu as a pivotal link between generations. Across all modes, the consistent verdict is that his forging combines precision with beauty, and his works are overwhelmingly — sound and well-preserved — testifying to the superior quality of his steel. He stands as a smith whose prodigious output was matched by unwavering excellence, and whose range of workmanship remains a defining measure of the school at its zenith.