Mutsu Daijo Miyoshi Nagamichi is the smith the published sources name as the de facto founder of Aizu , "会津新刀の事実上の祖," and one of his is dated Jokyo 2 (1685), the very year of his death, so that the blade can be read as a work of his final months. His house came to Aizu from the west: his grandfather Nagakuni resided at Matsuyama in Iyo and served Kato Yoshiaki, and when the Kato were transferred to Aizu in Oshu in 'ei 4 (1627), Nagakuni moved north in their retinue and Nagamichi's father Masanaga went with him. Nagamichi was born in Aizu in 'ei 10 (1633), studied under Nagakuni, and first signed Michinaga; on receiving the court title Mutsu Daijo in Manji 1 (1658) he changed his name to Nagamichi, and he died in Jokyo 2 at the age of fifty-three. One tradition makes him a pupil of Tsuda Sukehiro, but the published commentary finds his work closer to the Nagasone group, and Fujishiro rates him Jo-. The popular name he carries since, the Kotetsu of Aizu, is earned in the steel itself.
His characteristic hand is a into which are mixed, forming a of marked rises and falls, and in places two gunome run paired to give a gourd-shaped hyotan-ba, a configuration the published sources name as his forte and return to blade after blade. The enter thick and long and vigorously formed; gathers thickly, with coarser mixed in; runs through the with , and on his most active pieces appears near the base. The is bright and clear, the quality the commentary singles out as the constant of his good work. The published record draws the lineage comparison explicitly and repeatedly: this temper, it says, truly calls to mind Nagasone Kotetsu's so-called period, "正に虎徹のハネトラ時代の作柄を想わせる," and the , gently into a with at the tip and turning back somewhat deeply, is likened directly to Kotetsu's of that phase. Recognition of Nagamichi sits in both halves of that resemblance at once, the gourd-paired of the and the swept, deeply turning .
The is the steadier half beneath that active edge. The forging is , frequently mixed with and , often carrying a slight around the base and tending to stand, with thick adhering and fine entering well; on the most refined late the tightens to a and the lies very fine and dense, the at its clearest. Over it the most often opens with a straight, short -toned before broadening into the and of the body, the deep and the thick throughout. are usually absent, and where they appear it is no more than a run through as kaki-nagashi. The activity, not the ornament, carries the blade, and it is the and above all, working over the bright , that keep his robust from reading heavy.
His work resolves into one manner taken to two pitches. The first is the typical Kotetsu-toned hand, the with and , the paired hyotan-ba, and the swept that the published sources treat as his representative style. The second is the flamboyant peak of his best , in which, as the commentary puts it of one Heisei-designated blade, the is wider than usual and the shows marked height variation rich in change, "華やかな作柄を示しており," the thick and long, the thickly adhering, the and fully at work. He is, in the way the documentation runs, an open book rather than a mystery: nearly every designated blade is signed with a long signature, Mutsu Daijo Miyoshi Nagamichi, cut on an , and many are dated through the Enpo years and into Jokyo, so that his hand can be followed almost continuously from his title-taking to the year he died.
What sets him apart is drawn against Kotetsu, the smith he most resembles, rather than against a rival school. The published commentary marks the difference on a single explicit point: his work resembles Kotetsu in showing , but the tends toward a coarser quality, "沸の荒い点が相違する," and it is that coarser, more vigorous , together with the standing and the gourd-paired , that identifies the Aizu hand within the idiom. His own affirmative marks are the ones the record keeps naming: the hyotan-ba in the , the long thick , the and over a deep , and the bright of his finest pieces. The sources are candid about his limits as well, noting that many of his blades suffer from little curvature and a poor overall shape, against which his masterpieces stand out as the exception that also has a fine . As the de facto founder of Aizu he fixed the manner the later Aizu line would carry, a robust over an thick with , and his signed, dated and test-inscribed blades are the documentary spine of the school's beginning.
Nagamichi is rated Jo- by Fujishiro, with a Toko Taikan valuation of 600, and his standing among smiths is high for provenance. His designated record is eight blades, every one at the level, with none above it; he has no National Treasure or Important Cultural Property, so a Nagamichi is not held out of reach the way a designated heritage blade is, though it remains uncommon to encounter. Several of his carry gold-inlaid cutting-test inscriptions on the reverse by the tester Yamano Kanjuro Hisahide, recording cuts through bodies, and the published sources note that such a tested signature is itself rare and lends an excellent work additional value; of his supreme piece the commentary writes plainly, "この刀は彼の最高傑作で," the workmanship in both and outstanding, and of another that it is a bright and outstanding example, "地刃共に明るい三善長道出色の一口." The provenance behind one of his finest is among the most storied of any blade: it is recorded as bestowed by the Aizu domain lord Matsudaira Katamori upon Kondo Isami of the Shinsengumi for merit at the Ikedaya Incident, passing afterward to the Meiji general and sword connoisseur Tani Tateki and then into the Tosa Yamauchi family. A blade of his is also recorded at Dotsu Jinja. For a collector this is the open-book master of early : a signed, frequently dated and often test-cut that comes to market only from time to time, and a well-made example, bright in the and gourd-paired in the , rewards patience.