Kuniyasu (国安) was the next younger brother after Hisakuni and was known by the personal name Tozaburo. A smith of the school active in the period, his extant signed works are predominantly and . His display the classic period form — a slender build with , strong , and what the describes as a tendency for the blade to take on a slightly drooping feeling toward the tip (). His , by contrast, adopt a bolder silhouette with wide and , giving them what examiners characterize as a "powerful, assertive appearance."
In his forging, the identifies broadly two modes: one in which the stands out (), showing a somewhat coarse texture described as , with conspicuous large-grain patterns (o-) extending across both and ; and another that is tightly forged, with well compacted. Across both modes, forms abundantly. In tempering, his tend toward with slight in , accompanied by and , while his display large-scale o-wan- in deep , with and -ba intermingled. A characteristic feature shared with Kunitomo and noted repeatedly by the is a with an tendency — a soft, moist-looking quality identified as "an important merit characteristic of this smith." Many examples also show a tight spacing in the irregularities of the . Several works bear carved ornamentation, including carried through, , hatahoko, and motifs with lotus pedestals.
Kuniyasu's work is praised for clearly demonstrating his distinctive characteristics, with the singling out individual pieces for "especially fine workmanship in both and " that stands out even among this smith's oeuvre. The quality of the , consistently cited as a defining trait, positions him firmly within the lineage alongside Kunitomo, while the range from refined to bold attests to a versatile mastery of both restrained and vigorous tempering styles.