Sadamune (貞宗) of Province is traditionally said to have been a disciple of the great Masamune and later to have become his adopted son. His period of swordmaking extends from the very end of the period into the early period, placing him at the apex of the - as it reached full maturity. The consistently describes him as the smith who "most faithfully inherited his master's manner," yet the records are equally emphatic that clear differences distinguish master from heir: Sadamune's work is, on the whole, "calmer and more gentle in feeling" than Masamune's, and his blade forms tend toward a larger scale — wide , extended , and imposing proportions that reflect the transition into the era. He ranks, in the judgment of the , "among the foremost master smiths within the tradition."
Sadamune's forging characteristically presents (板目) mixed with (杢目), often with a flowing tendency and areas of standing grain. Exceedingly fine (地沸) is thickly applied, and (地景) enter frequently — sometimes in large, conspicuous patterns — so that the steel appears clear and luminous. The (刃文) takes a gentle, shallow (のたれ) as its principal motif, mixed with , , and , producing a restrained yet richly varied temper line. Along the edge, and appear; (金筋) and (砂流し) run through dependably; and the (匂口) is bright and clear. In places the becomes especially brilliant — "lustrous and beautiful " that "at times congeals and at times breaks up, displaying its activities to the full." The typically enters with or , showing vigorous , sometimes forming the flame-like appearance. Sadamune also favored carving (双樋) on both sides of his long swords, a convention the repeatedly identifies as distinctively his own. On and , elaborate relief carvings of , , and are executed with notable skill.
The recurring evaluative language across Sadamune's designations constitutes a remarkably consistent portrait. The praises his ability to "fully display the subtle and admirable qualities of " and to give "full expression to the fascination of workmanship," vividly revealing and within both and . His finest pieces are said to combine "the dignity and power characteristic of superior - workmanship" with a refined, high-toned that one likens, "in a single vein," to the master . Works by this smith that are bright and clear in both and , and moreover (健全) — sound and well-preserved — are singled out as "standing in the foremost rank." Several bear celebrated provenance through the Tokugawa shogunal house, the Maeda lords, and other great families, attesting to the esteem in which Sadamune's blades have been held from at least the early period to the present day.