Yamaura Kiyomaro was born Naizosuke Tamaki in Bunka 10 (1813) at Akaiwa village in Komoro, Shinshu, the second son of the rural warrior Nobukaze and the younger brother of the smith Saneo. He learned forging first under Kawamura Toshitaka, a swordsmith of the Ueda domain, signing his early blades Masayuki and for a brief interval Hidetoshi, the name his teacher had given him, before returning to Masayuki within the year. In Tenpo 6 (1835) he went up to under the patronage of the bakufu retainer and military scholar Kubota Kiyone, forged for a year at Choshu , returned to , and in the autumn of Koka 3 (1846) settled at Iga-cho in Yotsuya and changed his signature to Kiyomaro. He so excelled in the tradition that the published sources record he was called the Yotsuya Masamune (四谷正宗), and they place his reputation today as high as that of Kotetsu, calling him without question the foremost master among the . He died by his own hand at forty-two in Kaei 7 (1854).
What he aimed at, in the words of the published commentary, was the upper level of the transmission, his being the hand in which 「相伝上位」 is most fully reached, and among smiths his construction and manner reveal - with particular clarity. The temper is the tell. Over the he lays a mixed with , the entering, the thick and gathering coarse in clusters of , the whole work, as the puts it, 「覇気に満ちている」, filled with a vigorous and commanding spirit. Long and streaming run through nearly every blade he signed, in both his Masayuki and his Kiyomaro periods, the conspicuous activity of a built on rather than on clusters; the published sources single out this play of and in his strong steel as splendid. The answers the edge, turning pointed with , at times thrusting up to a point or settling into a small round.
The is the constant beneath all of this. He forges an that flows and stands a little, well packed and at times mixed with large open grain, the laid thick and in fine particles, the entering frequently and the steel clear. There is no ; this is a late hand reaching back over five centuries to , not a revival, and the brightness lives instead in the depth of the and the clarity of the . Where the forging tightens into the only grows clearer, and his mature carry an imposing shape, the body wide, the toward the point, the extended or running to a large point with the withered for a sharp impression.
His work is read across two periods and two registers. The earlier Masayuki blades, signed Masayuki, Minamoto Masayuki, Yamaura Tamaki Masayuki, and the bare single character Tamaki, show a tighter tending to , a mixed with , deep and well-attaching , the open document of his early years and his wandering through Choshu and Komoro. The mature Kiyomaro manner is the prime described above. Within it lies the register he prized most, the manner: the published sources call 「志津伝は得意中の得意」, the transmission his forte of fortes, naming one a - that shows variation in both and and stands among his representative works. That register gathers in the and he favoured and in the , where a base mixed with and tempers, with in clusters, into a brilliantly flamboyant .
What sets Kiyomaro apart from his contemporaries is exactly this reach. Where his peers copied or the dense steel of Kotetsu, he looked to Saburo Kaneuji and the masters, and the published commentary reads his aim as even in the early Masayuki hand. His own steel and edge, thick in and , vigorous in , profuse in and , set him apart by their force and brightness rather than by any borrowed pattern; the judges call one of his finest blades 「同作中の白眉」, the very best among works by the hand, and say of another that 「清麿の本領が遺憾無く発揮」, that his true ability is there fully revealed. He stands at the head of the Yotsuya line, the -revival manner carried forward through his pupil Kiyondo and the wider Kiyomaro-.
For the collector Kiyomaro is among the most sought of all the late smiths, and his record bears it out. Fujishiro grades him Sai-jo , and the Toko Taikan values his work high among names. He has no National Treasures and no Important Cultural Properties; his standing rests instead on the modern designation tiers, with two blades at , some forty-six at , and a further handful at the prewar Bijutsuhin. Extant works likely number a little over one hundred, and the published sources note that examples in ordinary with standard dimensions are comparatively few, and that a matched dated Kaei 1 is without parallel. The recorded blades pass through documented hands: the Iwasaki family and the Seikado Bunko that holds their collection, a retainer of the Matsushiro domain who commissioned a , the patron Kubota Kiyone for whom one Kiyomaro forged a , and the Bakumatsu swordsman Chujo Kinnosuke, whose favored sword one is said to have been. Most are held rather than traded, and a or Kiyomaro reaches the market only from time to time and at the very top of it; a signed example in private hands is among the more notable things a collector of could hope to encounter, a document of the moment when was reborn in .