Masahiro is, together with Masaie, a representative master of the Ko- school, which flourished in the district of Bingo Province from the late period through the era. Masahiro is traditionally said to have been the son of Masaie, the school's founder. Sword-signature reference works list six smiths of this name in Bingo Province and record dated works beginning with the Joji era (1362–1368), continuing through Shitoku, Kakei, and Oei; pieces bearing Oei dates are regarded as the work of a second generation. The lineage of the group extends as far as the end of the period. Because Bingo Province contained numerous shoen estates belonging to major temples and shrines of the Yamato heartland — among them To- and Rengeo-in (Sanjusangen-do) — it is surmised that interchange with Yamato was frequent. Accordingly, a pronounced Yamato temperament is naturally discernible in the style.
The workmanship of Masahiro is characterised by a -based temper executed in a distinctly Yamato-inflected manner. The forging is typically mixed with and , with a tendency toward (standing grain); fine adheres, enter, and a faint whitish appears. The is commonly a with a that tends toward tightness, accompanied by ; the shows fine , and such activities as , , and are observed. The characteristically turns back gently in , often with . However, compared with works made in Yamato proper, it is generally the case that the in both and is weaker. Two modes of are recognised in his work: one tending toward with a shallow , and another with a deeper turnback. Notably, certain works — such as the Shitoku 1 dated — display pronounced in the upper half, producing a or even sanjuba effect, representing a style in which the of both and is exceptionally strong. At times his work also reveals the influence of the neighbouring school; as the Shinkan Hiden-sho observes, pieces that "resemble the aspect of " blend Yamato character with -like features such as and .
Masahiro holds the Fujishiro rating of Jo-jo (superior-superior work). The repeatedly characterises his output as expressing the Yamato-flavoured qualities of the Ko- school with particular clarity. Among Ko- works, those attributed to his hand are frequently singled out as especially superior examples. His signed, are recognised as valuable material for the study of the working range and active period of the tradition. Extant dated works by Masahiro are exceedingly rare — only a small number, such as those of Shitoku and Oei, are confirmed — which lends added documentary significance to every surviving inscribed example. His signature, typically cut in large characters with a thick or fine chisel in a semi-cursive hand, is described as possessing an unforced, gentle character that is also forceful in feeling.