The oldest sword attributed to Yukiyasu is the preserved at Sanage Shrine in Aichi, an Important Cultural Property the published sources reach for as the earliest surviving example of the name. Yukiyasu is the chief name of the Ko-Naminohira school of Satsuma, the southern Kyushu line whose origin the published record traces to a smith called Masakuni, said to have come from Yamato to Naminohira in Taniyama District in the late period. No securely attributable work of Masakuni himself survives; his son Yukiyasu is the founder of the working line, and the name was then inherited generation after generation down into the late- era. The line is held to draw on the Yamato Senjuin tradition, and the published sources affirm that descent from the style of the work itself. The Yukiyasu under this entry is thus the early head of a centuries-long succession rather than one man, and the term Ko-Naminohira gathers the smiths and works of the school no later than the period.
His characteristic steel is an that flows and turns to a strong toward the edge, a viscous, soft the published sources call , with fine gathered thickly and entering, and a whitish, misty rising in the rather than the bright patterned reflection of . The old works of the school, the sources note, show a that runs to with an flavor. Over that the temper is restrained: a narrow , frayed at the with , run in with and frequent , fine and threading the edge, the clouded in an softness. The most telling departure from the Yamato manner the school otherwise resembles is at the base, where the temper drops markedly in a ; one early has it 'dropped greatly at the base' (元を大きく焼落す), and the runs straight to a with little turnback.
The is the constant across his every form and period. On the early signed the steel is dense and soft, one piece described with the steel having 'a , viscous feeling' (ねっとりした感がある); on the later broad work it stands a little more, somewhat blackish, the still rising. The narrow over it stays the school's quiet signature: an early compared with typical Naminohira shows less and richer activity within the edge, while the broad late pieces let the gather into a small in the lower half, mixing and , with the streak-like running intermittently from base to tip. Restraint, not display, is the rule; the published sources call one such blade 'restrained and deeply flavored in manner' (枯淡で味わい深い作柄).
His record divides cleanly into two faces of the one hand. The first is the slender, classical early- signed , small in , the high and wide, deep with marked , a thoroughly archaic silhouette whose four-character signature is cut crisply with a thick chisel on the upper . The second is the broad, powerful late- to work, long and wide with a high curvature, surviving or shortened. Beyond the the record carries a few other forms that confirm the hand: a signed in a long inscription and dated Kareki 2 (1327), with a plain carved on the , and a fully preserved , one of the school's few surviving examples. Dated and long-signed Yukiyasu being rare, these pieces are valued as documentary material as much as for their workmanship. The central scholarly difficulty is that the school's manner changes little with period; on the shortened attributions there is no single feature that must mean Yukiyasu, and the published commentary is candid that, as a general principle, 'the manner does not change with the age, and this is a point of recognition for this smith and his school' (作風が原則的に、年代によって変化しないのがこの工並びに一派の見処である).
What sets him apart he shares, in part, with his neighbours. The narrow , the soft steel, the and the at the base give his work an archaic Kyushu fragrance, and the published sources are careful to say it is not the school's alone: 'many show a at the , and all carry an antique fragrance,' a quality that 'is shared as well by other Kyushu classical hands such as Yukihira and Miike Mitsuyo' (此の派だけでなく行平や三池光世など他の九州古典派の作にも通じる). Against mainstream Yamato he is told by that dropped base; against by the absence of a bright patterned and by his whitish . His is a deliberately plain manner, and the judges name it as such: of one representative shortened they write that it is 'without flamboyance, yet a savor-worthy masterpiece firmly attributable to this smith, displaying a dignified presence' (派手やかさこそないものの堂々たる貫禄を示した滋味掬すべき同工極めの白眉).
For the collector Yukiyasu is a rare early Kyushu name, graded Jo-jo by Fujishiro. He has no National Treasures; his designated record runs instead through Important Cultural Property, the prewar Bijutsuhin, and the modern and tiers, eight blades in all standing in the and ranks. The two highest examples are an early signed and a later broad , the latter held the representative work of the school. Of recorded whereabouts, the earliest is preserved at Sanage Shrine, and the celebrated called Sasanuki passed in the Kabayama family, a branch of the Shimazu of Satsuma, so the school's history is bound up with its home province and its house. Surviving Yukiyasu are few and dated ones rarer still, so a signed Ko-Naminohira Yukiyasu comes to light only seldom; a privately held example, carrying the soft steel and dropped base and antique fragrance the published sources prize, is a notable thing for a collector to encounter, a document of how swordmaking began in the far south of Japan.