Masamitsu (政光) was a swordsmith of the Bizen Osafune school in the Nanbokucho period and one of the students of Kanemitsu. The NBTHK consistently situates him alongside fellow disciples Tomomitsu and Motomitsu as inheritors of Kanemitsu's manner. Among extant dated works, "the earliest extends to Enbun, while the latest reaches into Oei of the early Muromachi period," establishing an active career spanning roughly four decades across the transition from Nanbokucho to Muromachi. Dated inscriptions from Teiji 3 (1364), Eiwa 3 (1377), Oan 7 (1374), Koo 2 (1390), Meitoku 5 (1394), and Oei 6 (1399) provide an unusually well-documented chronological framework for his output, with later works showing a sugata that "leads toward the subsequent phase of so-called Oei Bizen."

While Masamitsu produced a variety of tempering styles -- notare, gunome, and suguha among them -- the NBTHK identifies his "particular point of interest" as the consistent tendency for the hamon to resolve into "comparatively small-patterned designs." The jihada is typically itame mixed with mokume, with fine ji-nie, delicate chikei, and a distinctive midare-utsuri; the steel occasionally takes on "a dark blackish tone." The hamon, centered on ko-notare, incorporates ko-gunome, kaku-gunome, ko-choji, and togariba in a tightly composed, small-scale midare that is "nioi-dominant with ko-nie." Fine sunagashi and small tobiyaki along the yakigashira appear as characteristic accents. The boshi enters in midare-komi, frequently becoming pointed at the tip with hakikake -- a feature that reliably "connects this work to Masamitsu's extant signed examples." Compared with Kanemitsu, "the irregularity here is somewhat reduced into a finer, smaller-patterned midare," and the bright nioiguchi is repeatedly praised.

Masamitsu's setsumei consistently commend his forging as meticulous and well-refined, noting that "the brightness of the nioiguchi is particularly noteworthy." The finest examples are distinguished by tempering "more complex, with greater variation" and an utsuri that stands "vivid," demonstrating that within the constraints of his characteristically small-patterned approach, Masamitsu achieved works of "showy and brilliant" effect. His varied constructions -- including kanmuri-otoshi-zukuri tanto and naginata-naoshi -- together with his abundant dated inscriptions, render him indispensable as documentary material for the study of late-Nanbokucho and transitional Oei-era Bizen smithing.