The Ko-Hoki school traces its origins to the celebrated Yasutsuna, active in Hoki Province during the late period and placed by modern scholarship as roughly contemporary with Munechika. From Yasutsuna descended a lineage of smiths -- his son Ohara Sanemori, and subsequently Sadatsuna, Aritsuna, Sanekage, and Yasuie -- who together constitute the group collectively referred to as Ko-Hoki, flourishing from the latter part of the period into the early period. The school's renown has been elevated beyond measure by the existence of the Dojigiri Yasutsuna, widely regarded as one of the supreme masterworks of the Japanese sword. These craftsmen represent the earliest fully developed phase of production outside the heartland, establishing a technical idiom in the San'in region that would prove foundational to the subsequent flowering of the tradition.
The Ko-Hoki manner is distinguished from contemporaneous work -- which it superficially resembles in its predominance of small-pattern -- by several diagnostic features that recur with remarkable consistency across the school's members. The characteristically displays mixed with and , with the grain standing prominently in a tendency, interspersed with and dark, mottled -like textures. The steel assumes a characteristically blackish kana-iro tone, and -- a mottled shadow pattern -- appears distinctly across the ground. The is built upon a foundation of or mixed with , , and shallow , thickly suffused with . Along the , the school's members produce a rich profusion of , , , and in places , generating what the describes as vigorous vertical activity at the boundary between hardened and unhardened steel. The consistently tends toward -- a moist, soft, slightly blurred quality -- with a or subdued character that stands in marked contrast to the brighter edge lines of . at the base of the temper near the is also encountered, further distinguishing the Ko-Hoki manner. Within this shared vocabulary, individual members express subtle variations: Yasutsuna's tempering encompasses the broadest range and strongest ; Sanemori's tends toward finer, more tightly arranged patterns; Sadatsuna introduces height variations and somewhat larger forms revealing a perceptible temperament; and Aritsuna maintains a more restrained with tight .
The Ko-Hoki school's historical significance extends far beyond its own production. The state explicitly that smiths such as Masamune and Norishige took the manner of work exemplified by this Hoki group as their ideal and, upon that foundation, established the - -- a lineage that would become one of the most celebrated traditions in Japanese sword history. The archaic flavour imparted by the interplay of standing , abundant , freely running and , and the distinctive blackish steel tone defines the aesthetic that later smiths would refine and transform. The consistently invokes an atmosphere of "archaic, artless dignity" and "rustic, provincial flavour" when characterizing these works -- a quality that, precisely because it is not affected or contrived, conveys what the examiners describe as "an ancient fragrance." Yasutsuna's position as the school's paramount figure is secured by the comparatively large number of signed works that survive and by the diagnostic consistency of his two-character signature. Sanemori's works, with their intimate scale and quiet authority, have drawn comparison with Kuniyasu and Ayanokoji Sadatoshi in the calm quality of their . Signed works by all members of the school are described as exceedingly rare, and blades retaining hold exceptional documentary value. Collectively, the Ko-Hoki oeuvre represents one of the most important bodies of work for understanding the diversity and depth of swordsmithing traditions in the formative era of the Japanese sword.