The Yamaura family rose from Akaiwa Village near Komoro, in district of Shinano, where the brothers were born to the gōshi (rural warrior) Yamaura Nobukaze. The trace the line through two smiths: the elder brother, born in Bunka 1 (1804), who signed Kanri and then Toshimasa under the gō Tenshi (天然子) before settling on the names Masao and Mao and, in his last years, Toshinaga; and the younger, born in Bunka 10 (1813), known first as Yamaura Tamaki and Ikkansai Masayuki (正行), briefly as Hidetoshi, and from the autumn of Kōka 3 (1846) as Kiyomaro (清麿). In Bunsei 12 (1829) the two entered the gate of Kawamura Toshitaka, official smith of the Ueda domain. Masayuki then went up to in Tenpō 5 to 6 (1834 to 1835), where the military scholar and hatamoto Kubota Seion (also read Kiyone) took him in and supported his maturing. A planned buki-kō (weapons association) collapsed and he withdrew to in Chōshū, forging there for a year from Tenpō 13 (1842); he later resided in Iga-chō of Yotsuya and became known to the world as "Yotsuya Masamune." The records place his aim squarely in the idiom of the smiths, into which he built his own hand.
A consistent vocabulary runs through the brothers' blades. The is of its period: broad with little taper, narrow with the upper often planed down, scant , deep sometimes tending to , and a markedly extended whose appears withered (kareru). The forging is , frequently dense mixed with and flowing into and near the edge; lies thick, enter freely, and the steel reads clear. Over this the smiths set a of round-headed mixed with -like elements, angular forms, and pointed () tendencies, the heights rising and falling; long enter, adheres strongly with patches of coarse , and the defining trait is the way long and run vigorously through a bright, clear . The enters in , turns pointed or with deep , and shows ; and small sometimes appear. The hand is recognized by this union of keen shape, dense -laden , and a restlessly active edge.
For the connoisseur the corpus fixes several anchors. Tang filing in with a finish marks the work up to about Tenpō 10 and 11, after which the is dropped for plain ; the early files even include a band of kiriyasu about a centimetre wide where the filing begins. The signatures move from Ikkansai Masayuki and Yamaura Tamaki Masayuki through Minamoto Masayuki to Kiyomaro, and dated and place-marked pieces, such as those reading "made at Castle" and "made at -Komoro Castle," document the Chōshū sojourn and the return through Shinano. The smith favored and in shorter blades, and and survive only rarely, prized as reference material. Several of the belong to the buki-kō commissioned group, one tied to the commissioner Tomo Kagetoku of Shinshū; an early Masayuki commissioned by Kubota Kiyone pushes the smith's documented contact with that patron back to his Matsushiro years. The elder brother's blades, signed in the Toshimasa period under the gō Tenshi, carry the -leaning with and in a quieter register. Within the register the line is read as the leading exponent of the -revival current of work.