Masaie (正家) is traditionally regarded as the founder of the school of Bingo Province and one of the representative figures of the group known as Ko-, which flourished from the end of the period into the period. According to and other reference works on smith lineages, Masaie was active around the Showa (1312--1317) or Shochu (1324--1326) eras, and his line continued down into the period. Within the Ko- group, Masaie stands alongside Masahiro as the school's most distinguished name. Works of the school display pronounced Yamato character, belonging firmly to the tradition centered in Bingo Province. An Imperial Collection bearing his signature has been described as representing the highest level of Ko- craftsmanship, with even Masahiro having scarcely any work of such caliber.
The distinguishing traits of Masaie's work may be seen in several key technical features. The typically shows tightly forged, with fine adhering and a characteristic whitish appearing in the ground metal---a hallmark of Ko- production. The favors , sometimes with a slight admixture of small , tempered in a -based manner with the tending toward tightness and present along the border. Fine and frequently appear within the tempered zone. Whereas many works by Masahiro are of , Masaie is often encountered in examples with a bold and imposing , lending his blades a particularly powerful .
Signed works by Masaie of early date are extremely rare, making authenticated examples of considerable scholarly value. His blades consistently demonstrate sound preservation, with both and described as notably in official evaluations. Among blades attributed to Ko-, his work is singled out as especially superior, and those examples bearing the large and characteristic make the attribution to Masaie fully persuasive. His contribution to the founding of one of Bingo Province's most important sword-making traditions secures his place among the significant smiths of the late period.