Masanobu (正信) is counted, together with Masaie and Masahiro, among the representative smiths of the Ko- school of Bingo Province. The lineage arose in the late period and flourished through the end of the period; works dating from the late through the period are collectively classified as Ko-. Signed works by Masanobu are exceedingly rare, yet examples bearing dates of Eiwa and Meitoku 5 (1394) have survived, placing him among those smiths who "adorned the finale" of the school.
A pronounced Yamato temperament is the defining hallmark of Ko- production, attributed to exchange with major Yamato temples whose landed estates were numerous in Bingo Province. The Ko- manner is readily discerned: standing out within an forging with conspicuous ; a with a tendency toward a tightened ; and a calm turning back gently in a rounded manner. Masanobu's works additionally display effects -- a feature shared with fellow smiths Masaie and Masahiro. His constructions frequently exhibit a high through which the Yamato character may be sensed, yet the Shinkan Hiden-sho notes an "appearance resembling ," confirming affinity with the neighboring school.
One signed transmitted in the Ii family of the Hikone domain demonstrates fine workmanship and constitutes precious documentary material. A dated inscribed Meitoku 5, formerly of the Maeda house of , is the sole example recorded in -period sword reference books. Rather than strong personal individuality, Masanobu's work embodies the collective Yamato-tinged character of his lineage, and signed examples remain of the highest documentary value.