Mondo-no-Sho Masakiyo is said to have been born in 10 (1670) at Izumi-go in Satsuma. His common name was Miyahara Seiemon, and he is also said to have been called Kakudayu. He learned forging from the Satsuma domain smith Maruta Sozaemon Masafusa, signing first Kiyomitsu and later Masakiyo; Honma's inventory of the Imperial collection adds that he may have signed Kageyoshi before that, a point it calls not yet fully studied. In the first month of Kyoho 6 (1721) he was summoned with his townsman Ippei Yasuyo by the eighth shogun Tokugawa Yoshimune to forge in . The bakufu granted him the right to cut the single-leaf hollyhock crest on his tang, and on the journey home the court raised him to the title Mondo-no-Sho. The published sources give his death in Kyoho 15 (1730) at sixty-one, while the Honma inventory gives sixty-six. They place him with Yasuyo as "the twin pillars of Satsuma ".
His characteristic work is the modelled on the old manner, which the published sources call "the -style range he handled with greatest mastery". He tempers a into which he sets , and pointed , with and entering. The is deep and the thick and strong, with coarse mixed in and gathering unevenly. Long, frequent and run through the , accompanied by , and the is bright and clear, only here and there a little uneven. The Honma inventory records that some of his blades, once shortened, "have come to pass as Masamune or ".
The is an that flows strongly overall and turns -inclined, at times standing a little with mixed in, at times a tight . It carries thick with coarse mixed, and the commentary describes vigorous of a distinctive, kawarigane-like character. The runs in or to a pointed return, swept with vigorous carrying long , and turns back deeply; on some blades it ends in a . His body is the grand Satsuma form, extremely wide with a thick , ample and an extended . Of such a blade the published sources write that its robust bearing "gives the feeling of a decisive downward cut".
On his most ambitious pieces the published sources single out a further feature and read it as antique. Especially in the upper half, gather vigorously at the crests of the temper and present an appearance like . In their words, "the manner in which are vigorously applied at the crests of the temper to produce a -like appearance conveys an impression of antique flavor". This is the upper reach of the same hand rather than a separate manner. His tang is almost always , tapering to an or sword-shaped tip with shallow file marks and a large long signature, often with the hollyhock crest and a date. Blades signed Kiyomitsu are extremely rare, and one in the Honma inventory carries a second inscription on the reverse, cut after he received his title. Those signed Satsuyo Kafu ju likewise predate the title. The inventory finds the five-character signature Mondo-no-Sho Masakiyo in greatest number and calls one such "a considerable masterpiece copying the manner". The published sources also note that in his later years many blades were made as by his son Masachika and his pupil Masamori; the inventory reads his dated Kyoho 15 as a by Masachika and probably Masachika's own work.
Within his province he is read against Yasuyo. Where Yasuyo often tempered a calm -toned , Masakiyo tempered the varied -style , with its pointed , its coarse and its long running . His gathering and the antique they form are further traits of his own. The published sources say that his best work can at times be mistaken "for old superior blades".
He has no National Treasures and no Important Cultural Properties. His record runs through twenty-two blades in the and tiers, one of them , and four recorded in Honma's inventory of the Imperial collection, twenty-six designated works on record and all of them signed. His provenance reaches the great houses of his age. The , dated Kyoho 9, was presented with a blade by Yasuyo by the Kagoshima lord Shimazu Tsuguhisa to the Minister of the Left Konoe Iehisa, who sent both smiths fine silver and a set of the Six Immortal Poets inscribed by court nobles; the documents survive. Another , forged in Kagoshima in Kyoho 9 on the shogun's order with Yasuyo, was presented to the bakufu the following year and long remained with the Tokugawa house. Most designated blades are held rather than traded. A fine signed Masakiyo in his -style manner comes to market only from time to time and with patience, and a dated, crest-bearing in his full manner remains a landmark acquisition.