Naminohira Yukiyasu is the principal name of the Naminohira school of Satsuma Province, a lineage traditionally held to descend from the Yamato Senjuin line. According to established accounts, a smith named Masakuni migrated from Yamato to Naminohira in Taniyama District, Satsuma, around the Eien era (987–989) of the late period, becoming the founder of the school. His son was called Yukiyasu, and thereafter successive generations inherited the name, the main line continuing without interruption from the period through to the era. The collective term Ko-Naminohira designates those smiths and works that do not descend beyond the period. The oldest surviving work attributed to the name is the at Sanage Shrine, dated to the late period; next in renown is the known by the go "Sasanuki," transmitted in the Kabayama family, a branch of the Shimazu clan. The notes that the school's workmanship "strongly suggests a Yamato temperament," and its stylistic kinship extends to other Kyushu classical lineages such as Bungo Yukihira and Miike Mitsuyo.
The forge work of Yukiyasu is characteristically tending toward , with inclination especially near the edge, and in older works an -like flavor may appear in the . The steel conveys a distinctive — viscous, sticky — feeling, with fine adhering thickly and entering throughout. stands out in many examples. The is based on slender , at times carrying a shallow tendency or mixing in elements; adheres well, with , , and frequently intermingling. Fine and appear, and from base through tip, faint streak-like activities form intermittently. The characteristically shows an — moist, soft — tendency, a trait the identifies as among the most diagnostic features of the school. Conspicuous at the base is another hallmark; the is typically tempered straight, tending toward . Compared with typical Yamato work, the in both and tends to be very fine, lending the blades a subdued, intimate character rather than a bold one.
The consistently describes Yukiyasu's works in terms of restrained depth — a "plain and unpretentious style" that nonetheless possesses "a dignified presence and deep, savor-worthy charm." The phrase (restrained elegance) recurs alongside the observation that these blades display "a restrained yet deeply flavored style." Although they lack flamboyance, the examiners note that the streak-like activities within the tempered edge are "especially noteworthy as an element that adds interest." It is further observed that "an antique fragrance pervades such works," and that the school's manner "shows little change according to period," making precise chronological assessment difficult — a testament to the tenacious conservatism of the tradition. Several surviving blades bear traces that "evoke remembrance of old martial exploits," while rare signature placements and date inscriptions afford "high documentary value." As the representative master of Ko-Naminohira, Yukiyasu occupies a foundational position within the Satsuma forging tradition, his work embodying the deep, quiet dignity of Kyushu's oldest sword-making lineages.