Kunitsuna was a swordsmith of the group in Kyo of Yamashiro Province. He styled himself Toroku Sakon and was the youngest of six brothers, the eldest being Kunitomo. It is transmitted that he later went down to in Province and, together with smiths Sukezane and Kunimune, became one of the pioneers who opened the way for smithing. Traditions vary as to whether the one who summoned him was Hojo Tokimune or Hojo Tokiyori. At present, extant works that can be affirmed with confidence as authentic signed pieces by this smith are extremely few; his renown is elevated all the more by the existence of the celebrated Kunitsuna, an Imperial heirloom. Among works to which all would point as unquestionably genuine, three stand foremost: the ; a blade formerly in the collection of the Viscount Nishitakatsuji family; and an Important Art Object formerly owned by the Aizu Matsudaira family, which, although some sources state it was lost to wartime fire, in fact survives intact.
works are generally characterized by a serious and refined elegance, yet Kunitsuna alone is distinctive within the group. His shows pronounced without the blade assuming a drooping tendency toward the tip. The forging displays comparatively large with a strongly standing and thickly laid , frequently accompanied by and, in many instances, a -like that appears below the . His tends to be broad in , with a foundation into which , , and shallow are intermingled; thick and enter vigorously, the is distinctly deep, and within the temper forms both deeply and thickly. , , and are interwoven throughout, producing richly varied . The manner in which both and are vigorously animated is precisely the hallmark of his art, and the conspicuous strength of the stands out as a defining trait that separates his work from the quieter, more restrained character of his brothers.
In terms of workmanship, two distinct manners may be observed: works that follow the refined idiom with tightly forged and calm , and others of a markedly different character — powerfully built, with robust form and a more standing texture in the . The belongs to the latter type, while certain signed pieces and traditionally attributed blades represent the former. This breadth of stylistic range, together with the rarity of securely signed examples, has long made Kunitsuna a subject of particular scholarly interest and has ensured that each newly confirmed work constitutes valuable material for understanding the full extent of his art. His role as a bridge between the classical refinement of the Yamashiro tradition and the vigorous spirit that would come to define early forging places him at a pivotal juncture in the history of the Japanese sword.