Masahiro was the son of Yoshinobu, a smith of the collateral line who first signed Masanaga and took the name Masahiro in 'ei 2 (1625). He worked at Saga in the orbit of the school, served as a close attendant of the second-generation Omi no Daijo Tadahiro, and after the death of the first-generation assisted the second generation as, in the words of the published sources, a most able collaborator. Later he received the court title Kawachi Daijo, signing no Kawachi Daijo Fujiwara Masahiro. Of the date the published record is candid: although tradition gives 'ei 5, works dated as late as 'ei 16 still sign only no Saga-ju Masahiro, and the title first appears on blades dated the eighth month of 'ei 18, so the modern view places the appointment about that year. Among the waki-, the branch smiths working outside the main house, the holds him the most accomplished of all, 「傍肥前の中でも最も技量が優れており」.
What distinguishes him is exactly what sets him against the main line. Where the house is read first in its calm, deep- , Masahiro favored the opposite, and the published sources state it plainly: 「作風は乱れた刃を好んで焼き」, his hand favored the irregular temper. His characteristic begins with a at the and rises into a -dominant , mixing , - and large with and at times a or angular flavor. The clove pattern the judges liken to that of no Daijo Tadahiro. The temper is set high and low, in places linking clusters of with a quieter -toned line, long and entering well; the is deep, with thick gathering in the valleys of the , a little and at times , running well and long appearing. On one such the published sources write that he forges the he excelled in and shows his true ability to full effect.
Beneath that flamboyant edge lies the refined steel he shares with the rest of the school. The is a tightly packed becoming the , the rice-bran skin: a dense with dust-fine laid thickly and fine entering well, bright and clear. The runs straight to a with and a long, deep turnback, at times opening into a small on the . The is the well-balanced shape, at times wide in body with an extended or large , powerful and forceful. The stays bright over both his showy and his quiet work, the constant of his and .
He was not, however, a smith of one manner only. A clear register of his record is the he also commanded, a quiet toned with a shallow and mixing , and entering, fine and naturally interwoven, the bright over the well-packed . One of 'ei 11, worked in this calmer manner, the published sources name his finest, 「この刀はその白眉である」. His dated works survive only in small number, running from 'ei into , and several pieces whose signatures blend his pre-title and post-title styles are valued for fixing the chronology of his career; he is said to have died at fifty-nine in 5 (1665).
His distinction from the main house is drawn by the judges themselves. He is set apart not only by his preference for over but by his , which differ from the main line's, and by his consistent practice of signing on the . The published sources read his blades as carrying a more natural vigor and driving spirit than the main house, 「本家忠吉家の作よりも自然、覇気のある作が多く」, and one entry says of a representative piece that he forges the at which he excelled and displays his true ability without reserve, 「彼が得意とした乱れ刃を焼いて、その本領を遺憾なく発揮している」. He stands, then, as the most gifted of the branch hands, the one among the waki- whose work most readily approaches the main line in quality while keeping a manner distinctly his own.
For the collector Masahiro is a desirable and attainable name. Fujishiro grades him Jo-jo . He has no National Treasures and no Important Cultural Properties; his record runs instead through the rank, where some thirty of his blades have been designated, the published sources calling his finest powerful and forceful in both and and richly animated. Documentary interest is high among them: one carries within a a relief of Shigetsu Hotei by the carver Yoshinaga, a design the published sources call extremely rare among blades and of notable value for the study of the province's carving. Provenance is only partly recorded, so it is best stated quietly: his blades are held in private collections of recorded whereabouts rather than in a roll of famous houses. A signed Masahiro is not beyond the reach of a serious collector as a top main-line blade can be, and from time to time, with patience, one of his works comes to light, a chance to hold the flamboyant of the most accomplished of the waki-.