Kiyotsuna is the de facto founder of the Nio school of Suo Province. The lineage is traditionally said to have begun around the Hoden era (1135–1141) with Kiyozane or Kiyohira; however, "no secure surviving works by these putative founders are known, and today Kiyotsuna is regarded, in effect, as the school's founder." Among his extant works, the earliest is a tachi at Itsukushima Shrine bearing a written-out inscription reading "Bun'ei 2, third month — Kiyotsuna" (1265), followed by a tanto signed "Boshu Kuga-sho Kiyotsuna" dated Kenmu 2 (1335). Thereafter, smiths using the same name continued in an unbroken line through the Muromachi period and even into the shinto era. The appellation "Nio" most persuasively derives from residence in Niho-sho within the province. Several smiths are thought to have used the name from the mid-Kamakura through the Nanbokucho period, placing the first generation's active career in the late thirteenth to early fourteenth century.

Suo Province contained many temple estates belonging to major Yamato monasteries, beginning with Todai-ji, and "the strongly Yamato-colored character of Nio workmanship reflects exchange with the Yamato heartland." The NBTHK consistently identifies the school's individuality through two diagnostic traits: the appearance of shirake-utsuri — a whitish, hazy reflection — in the forging, and the tendency for the hamon to show urumi, a moist, soft quality in the temper line. The kitae is characteristically itame-hada mixed with mokume, tending toward standing grain, with fine ji-nie and chikei. The hamon is based on suguha — often narrow or slender — mixed with ko-gunome, displaying ko-ashi, ko-nie, and such activities as kinsuji, sunagashi, hotsure, and uchi-noke. The boshi is consistently straight, returning in ko-maru, sometimes with hakikake toward the tip. Construction frequently shows a high shinogi, somewhat thick kasane, and taka-no-ha file marks — features that "present a manner that also accords with Yamato workmanship."

Across the body of designated works, the NBTHK repeatedly affirms that Kiyotsuna's blades "clearly express the characteristics of the Nio group" while displaying "superior workmanship" and "excellent" overall quality. Signed examples with ubu-nakago are singled out as "precious as documentary material" and possessing "exceptionally high value as reference material for study," reflecting the rarity of securely attributable works by this smith. The tachi form — slender, with pronounced koshizori and ko-kissaki or chu-kissaki — is consistently praised for conveying "the elegant tachi sugata of the late Kamakura period." Blades in sound condition are noted as kenzen, retaining ample hiraniku with "not the slightest loosening in either ji or ha." At a glance, the workmanship is "suggestive of Yamato proper," yet the persistent presence of shirake-utsuri and urumi distinguishes the Nio school as an independent lineage — one rooted in provincial temple culture yet possessed of unmistakable individual character.