The Yasumasa lineage, known as the Hosho school, resided in Takaichi District of Yamato Province and flourished from the mid- period through the era. Among its representative smiths, Sadamune and Sadayoshi are the most widely renowned; it is said that both used the common name Yasumasa Goro. Additional skilled makers include Sadakiyo, Sadako, Sadamitsu, and Sadahiro, all of whom share the character (貞) as a generational element in their names. Within the Hosho lineage, bearing reliable signatures are extremely rare; signed pieces are, however, occasionally encountered among by Sadayoshi, Sadamune, Sadakiyo, and Sadakatsu. Inscribed dates such as Bunpo, Genko, and Karyaku are seen on works by Sadayoshi, placing the group's principal activity squarely in the late period. A Kochu dated Shotoku 1 (1711) recording "Yasumasa Goro" and valuing a blade at thirty gold coins attests to the enduring esteem in which this lineage was held by subsequent generations of appraisers.
Among the five Yamato schools, the Yasumasa group displays the most individual style. Their forging conspicuously reveals an orderly , often with a tendency toward standing grain; adheres thickly and abundantly, is intermingled, and in some cases -ware develops, producing a pronounced standing-grain appearance that gives the steel a strong, hard character. In earlier works, the within the ground is particularly thick and the more prominent, while frequently stands along the grain. The is characteristically -based, at times mixing shallow , , or ; along the edge appear , uchi-noke, , , and , while adheres well and fine and run throughout. A distinctive feature is the tendency for the to broaden from around the upward. The is finished with vigorous ending in , a hallmark that, together with the forging and on the tang, makes the school's manner among the most readily identifiable within the Yamato tradition.
The Yasumasa group's oeuvre encompasses , , , and in a range of constructions including , , , and , the last reflecting conversions. Blades attributed to this lineage consistently display a bold and robust construction, and the finest examples demonstrate both and that are bright and clear, evoking the elegant taste characteristic of Yamato craftsmanship. Provenance records attest to distinguished ownership: one blade is documented as having been presented by Okudaira Masanobu to Date Masamune, thereafter passing to his eldest son Hidemune and transmitted within the Uwajima Date family. Even among works that have been greatly shortened and rendered unsigned, the characteristic features of the Yasumasa group remain unmistakable, and the best examples are preserved in condition with the overall workmanship of notably fine quality.