Among the dated tantō by Masamitsu is one carved on the omote with a swelling-dragon kurikara and on the ura with a bonji and gomabashi, a thick-kasane piece dated Eiwa 4 (1378) that the published record calls a representative superior work of his oeuvre[[c:1]] and that has come down with the epithet Koryū Masamitsu, the Small Dragon Masamitsu. He was a Bizen Osafune smith of the mid-Nanbokuchō into the early Muromachi period and one of the disciples of Osafune Kanemitsu, named in the published sources in one breath with his fellow students Tomomitsu and Motomitsu. His dated blades run from Enbun through Ōei, so that his working span is fixed with a clarity unusual for the late Osafune, and he carries his teacher's manner forward into the closing decades of the koto Bizen tradition.

The tell of his hand is restraint. Following Kanemitsu he works notare, gunome-midare and suguha alike, yet across the whole of his output the temper settles toward a small, subdued pattern, and the NBTHK names this exactly: 「総じて刃文が小模様となるところに此の工の見どころがある」, the point of appreciation in his work is that the hamon as a whole becomes small in scale. Over a well-forged itame he tempers a ko-notare into which gunome, kaku-gunome, ko-chōji and pointed togariba enter, the nioiguchi nioi-dominant and tight, carrying ko-nie with fine sunagashi and kinsuji, and on his finest tantō, the Koryū Masamitsu among them, he sets a kataochi-gunome, the saw-tooth temper that is the Kanemitsu school's own inheritance. The ashi and yō enter well; the activity is held within a quiet line rather than flung into towering clusters.

The jigane is the Osafune constant beneath that quiet edge. His itame is well forged, often standing a little and mixed with mokume, with a thick ji-nie and fine chikei, and over it stands a bright midare-utsuri, the speckled reflection of old Bizen steel, that the published record finds on his signed and his attributed work alike. Where the forging tightens into a packed ko-itame the utsuri only grows clearer; on the slender late pieces it can run as a straight bō-utsuri or a sugu-utsuri instead. The bōshi answers the hamon, entering in midare-komi to a ko-maru or finishing with a faintly pointed togari-gokoro and hakikake, and on his tantō he carves the devotional program of the school, bonji with a gyō-form kurikara and bonji with gomabashi, the swelling-dragon motif that the published commentary traces to the distinctive horimono of the Osafune line since the second-generation Nagamitsu[[c:2]].

His record falls into clear registers. The signed and dated work of the high Nanbokuchō is the core, cut on an ubu tang with the full Bishū Osafune Masamitsu signature and a year date. The late work is the slender kodachi, ko-tachi and naginata of the Kakyō years at the very end of the period, narrower in body and tighter in the line, which the swordbooks gather as a class the published record describes thus: 「総称して江戸時代以来小反物と称している」, pieces collectively called ko-sorimono since the Edo period. Beside these stand the ō-suriage mumei katana and naginata-naoshi attributed to him within the Kanemitsu circle. Running through all of it is the standing scholarly note that the name Masamitsu was borne by two generations, the shodai of the Enbun through Eitoku years and the nidai of the Kakyō years, the swordbooks assigning individual pieces to each by year inscription and workmanship; on one signed second-generation tantō the judges go so far as to write that the quality of its ji and ha is so good as to give 「殆んど兼光を見るような感がある」, almost the impression of looking at Kanemitsu himself.

What sets him apart within his own school is precisely that subdued line and that bright reflection. On the ō-suriage attributions the published record affirms the Kanemitsu-school ji and ha while granting candidly that the work resembles Kanemitsu yet falls a step short of him, seen in the slightly subdued temper and the less settled monouchi, so that the attribution rests on era and school as much as on a personal tell. Against his teacher's broader, more varied midare, Masamitsu is read by the smallness of his pattern and the tightness of his nioiguchi; against the plainer late-Bizen hands he is held by the brightness of his midare-utsuri and the kataochi-gunome on his edge. He stands among the last Osafune masters to keep the Kanemitsu manner intact before the school turned to the volume production of the Ōei years.

For the collector he is a knowable late-Osafune name carried on a substantial signed record. Fujishiro grades him Jō-jō saku. He has no National Treasures; his standing rests instead on two Important Cultural Property tachi, two blades at the Tokubetsu Jūyō rank, and a wide spread at Jūyō, and the published commentary singles out one Tokubetsu Jūyō tachi, more complex and showy than his wont, as 「同作中出色の出来映え」, an outstanding example among his works. His blades are grounded in old provenance, the Tokugawa shogunal house among them, with the Koryū Masamitsu tantō transmitted in the Ōmaeda family and once carrying a Hon'ami Kōtsune origami, and his work is held today in long-standing public and private collections, including the Kyushu National Museum, the Hayashibara Museum of Art and the Tokyo National Museum. With only a small number of blades in the Tokubetsu Jūyō and Jūyō tiers and most of those long held rather than traded, a signed and dated Masamitsu of recorded whereabouts comes to light only from time to time, and a privately held example, ideally an ubu-tang piece with its date intact, is a satisfying thing for a collector to encounter, a precisely datable document of how the great Osafune line carried its art to the close of the koto age.

Among the dated tantō by Masamitsu is one carved on the omote with a swelling-dragon kurikara and on the ura with a bonji and gomabashi, a thick-kasane piece dated Eiwa 4 (1378) that the published record calls a representative superior work of his oeuvre[[c:1]] and that has come down with the epithet Koryū Masamitsu, the Small Dragon Masamitsu. He was a Bizen Osafune smith of the mid-Nanbokuchō into the early Muromachi period and one of the disciples of Osafune Kanemitsu, named in the published sources in one breath with his fellow students Tomomitsu and Motomitsu. His dated blades run from Enbun through Ōei, so that his working span is fixed with a clarity unusual for the late Osafune, and he carries his teacher's manner forward into the closing decades of the koto Bizen tradition.

The tell of his hand is restraint. Following Kanemitsu he works notare, gunome-midare and suguha alike, yet across the whole of his output the temper settles toward a small, subdued pattern, and the NBTHK names this exactly: 「総じて刃文が小模様となるところに此の工の見どころがある」, the point of appreciation in his work is that the hamon as a whole becomes small in scale. Over a well-forged itame he tempers a ko-notare into which gunome, kaku-gunome, ko-chōji and pointed togariba enter, the nioiguchi nioi-dominant and tight, carrying ko-nie with fine sunagashi and kinsuji, and on his finest tantō, the Koryū Masamitsu among them, he sets a kataochi-gunome, the saw-tooth temper that is the Kanemitsu school's own inheritance. The ashi and yō enter well; the activity is held within a quiet line rather than flung into towering clusters.

The jigane is the Osafune constant beneath that quiet edge. His itame is well forged, often standing a little and mixed with mokume, with a thick ji-nie and fine chikei, and over it stands a bright midare-utsuri, the speckled reflection of old Bizen steel, that the published record finds on his signed and his attributed work alike. Where the forging tightens into a packed ko-itame the utsuri only grows clearer; on the slender late pieces it can run as a straight bō-utsuri or a sugu-utsuri instead. The bōshi answers the hamon, entering in midare-komi to a ko-maru or finishing with a faintly pointed togari-gokoro and hakikake, and on his tantō he carves the devotional program of the school, bonji with a gyō-form kurikara and bonji with gomabashi, the swelling-dragon motif that the published commentary traces to the distinctive horimono of the Osafune line since the second-generation Nagamitsu[[c:2]].

His record falls into clear registers. The signed and dated work of the high Nanbokuchō is the core, cut on an ubu tang with the full Bishū Osafune Masamitsu signature and a year date. The late work is the slender kodachi, ko-tachi and naginata of the Kakyō years at the very end of the period, narrower in body and tighter in the line, which the swordbooks gather as a class the published record describes thus: 「総称して江戸時代以来小反物と称している」, pieces collectively called ko-sorimono since the Edo period. Beside these stand the ō-suriage mumei katana and naginata-naoshi attributed to him within the Kanemitsu circle. Running through all of it is the standing scholarly note that the name Masamitsu was borne by two generations, the shodai of the Enbun through Eitoku years and the nidai of the Kakyō years, the swordbooks assigning individual pieces to each by year inscription and workmanship; on one signed second-generation tantō the judges go so far as to write that the quality of its ji and ha is so good as to give 「殆んど兼光を見るような感がある」, almost the impression of looking at Kanemitsu himself.

What sets him apart within his own school is precisely that subdued line and that bright reflection. On the ō-suriage attributions the published record affirms the Kanemitsu-school ji and ha while granting candidly that the work resembles Kanemitsu yet falls a step short of him, seen in the slightly subdued temper and the less settled monouchi, so that the attribution rests on era and school as much as on a personal tell. Against his teacher's broader, more varied midare, Masamitsu is read by the smallness of his pattern and the tightness of his nioiguchi; against the plainer late-Bizen hands he is held by the brightness of his midare-utsuri and the kataochi-gunome on his edge. He stands among the last Osafune masters to keep the Kanemitsu manner intact before the school turned to the volume production of the Ōei years.

For the collector he is a knowable late-Osafune name carried on a substantial signed record. Fujishiro grades him Jō-jō saku. He has no National Treasures; his standing rests instead on two Important Cultural Property tachi, two blades at the Tokubetsu Jūyō rank, and a wide spread at Jūyō, and the published commentary singles out one Tokubetsu Jūyō tachi, more complex and showy than his wont, as 「同作中出色の出来映え」, an outstanding example among his works. His blades are grounded in old provenance, the Tokugawa shogunal house among them, with the Koryū Masamitsu tantō transmitted in the Ōmaeda family and once carrying a Hon'ami Kōtsune origami, and his work is held today in long-standing public and private collections, including the Kyushu National Museum, the Hayashibara Museum of Art and the Tokyo National Museum. With only a small number of blades in the Tokubetsu Jūyō and Jūyō tiers and most of those long held rather than traded, a signed and dated Masamitsu of recorded whereabouts comes to light only from time to time, and a privately held example, ideally an ubu-tang piece with its date intact, is a satisfying thing for a collector to encounter, a precisely datable document of how the great Osafune line carried its art to the close of the koto age.