The Nagato Sa school carries the Samonji manner westward, out of its Chikuzen home and into the province of Nagato (the territory the smiths name in their signatures as Choshu). Its origin is a single relocation: Yasuyoshi, the son of O-Sa and second generation of the Sa line, is traditionally said to have moved from Chikuzen to Choshu, an account anchored by an extant tanto dated Shohei 17 (1362) inscribed Choshu-ju Yasuyoshi. From him the name passed down through the late Nanbokucho and into the early Muromachi period, the descendants and students who continued it gathered under the collective reading "Choshu Sa." Akikuni is the chief of those continuators, transmitted as a disciple taken on after Yasuyoshi carried the Sa name into the province; the reference works on signatures list six smiths who bore the Akikuni name, beginning with a Bunwa-era hand of the Yasuyoshi line and reaching to an Oei-period smith described as the son of Choshu Yasuyoshi, so that the name is best read as one handed down through the Nagato workshop. The school is therefore a provincial, late branch of the Sa tradition, working a country forge in an old manner whose dated examples run from the Shohei and Eiwa years through Oei and into Bunan.

In the forge the members describe a common vocabulary. The kitae is itame mixed with mokume and nagare-hada, the grain often standing toward hada-dachi, with thick ji-nie and fine chikei-like lines of steel; a whitish shirake-utsuri is named as a hallmark, and the ground steel frequently shows a somewhat dark, iron-like tone rather than the bright Chikuzen ji. The hamon divides into a quieter suguha mode and a representative midare manner: shallow ko-notare mixed with gunome, the gunome running linked in a connected pattern the smiths call tsure-gokoro, with ashi and yo entering, ko-nie adhering, and fine kinsuji and sunagashi drawn through; the temper is mainly nioi-dominant with the nioiguchi tending to sink. The boshi enters midare-komi with a pointed tendency and a long kaeri, at times a ko-maru swept in hakikake. Within this shared frame the members diverge by degree: Yasuyoshi's finest pieces forge compact and bright, retaining the Sa school's character most clearly, while Akikuni's run coarser and more nie-driven, his broadest katana carrying a rustic (yashu) cast and, with a large kissaki, a vigorous and commanding spirit.

To kantei a Nagato Sa, read the school against its Chikuzen source. The setsumei consistently note that the work does not match O-Sa in the brilliance of both jigane and temper; the standing grain, the shirake-utsuri, the darker steel and the sinking nioiguchi mark the peripheral western forge, and the manner sometimes does not connect directly to Yasuyoshi's own style, the attribution resting on a transmitted current of workmanship rather than a close stylistic tie. Signed works are comparatively few, which lends the surviving inscriptions particular documentary value: a date and a place-name (Choshu-ju Yasuyoshi, or Choshu Setozaki junin Akikuni, sometimes with the title Saemon no Jo, sometimes folded over as an orikaeshi-mei) do as much to anchor a piece as the temper, the more so because several Akikuni share the one name. Yasuyoshi is the senior hand of the group, his sugata larger and more imposing than his father's with wide mihaba and thin kasane; Akikuni follows as a well-documented branch smith, graded jo saku, whose large-scale blades are scarce and valuable for fixing the chronology of production. Provenance, where it survives, reads like the local history of the blade: Yasuyoshi's work descended in the Inshu Ikeda and Maeda houses, and Akikuni's in the Ouchi of Suo and Nagato and the Mori who succeeded them, the western great houses keeping the western Sa to themselves.