Masatsune was born at Nodo in Mino Province and first signed Kanetsune, a smith of the Seki tradition who carried that Mino root into the new swords of Owari. The published sources follow his career in unusual detail. In Eiroku 10 he set up an independent branch and moved to Komaki village, changing his name to Masatsune around that time; in Tensho 19 he received the court title Sagami no Kami; in Keicho 5 he followed Matsudaira Tadayoshi to Kiyosu, and he became a retained smith of the Owari Tokugawa house. In Keicho 12 he took the tonsure and retired, passing the name Sagami no Kami Masatsune to his son, but when the second generation died suddenly two years later he returned to the forge, and from that time he signed Masatsune Nyudo. He died in Genna 5 at the age of eighty-four. In later generations he was counted among the Owari Sansaku, the three founding smiths of Owari shinto, beside Hoki no Kami Nobutaka and Hida no Kami Ujifusa.

His recognized hand is the bright straight temper of his hira-zukuri tanto and wakizashi, the form in which his surviving work is most numerous. Over a tightly forged ko-itame mixed with mokume, the steel flows toward masame and carries thick ji-nie, with fine chikei entering and, on several pieces, a mizukage-like feature rising diagonally from below the machi. The temper is a chu-suguha, at times a wide suguha, laid in ko-nie, into which small gunome enter with ko-ashi. What separates his suguha from a plain Seki straight temper is the worked habuchi: it frays into hotsure, with nijuba, kuichigai-ba and uchinoke mixed in and fine sunagashi running through, while the nioiguchi stays bright. The published commentary calls one such tanto a thoroughly characteristic example, with 「相模守政常の典型的な直刃の作例」[[c:1]] (a typical example of Sagami no Kami Masatsune's suguha).

The jigane is the constant beneath both of his manners. It is an itame that overall tends toward masame, with ji-nie attached and, on the better tanto, chikei standing out and the steel reading bright. Where the forging tightens into ko-itame mixed with mokume the impression is of strength, and the published sources single out the diagonal mizukage at the machi and the abundant ji-nie as the marks of his sound forging. On the wakizashi the grain at times stands a little, with the upper half flowing toward the mune, and the carvings he favours, a suken or bonji above the koshimoto with gomabashi on the reverse, are described as crisp and well harmonised with the blade.

His second manner is the Owari-Seki wet temper, carried on his katana, naginata and yari. Over an itame that flows into masame with ji-nie, he tempers a wide suguha tone or a shallow notare-gunome base with togariba and small gunome mixed in, ashi and yo entering, the nie sometimes coarse and gathered in clusters, kinsuji and sunagashi seen, and the nioiguchi tending to a subdued shizumi. The published sources name this directly: on his large Keicho-form katana they read 「尾張関得意の濡れ刃」[[c:2]] (the wet temper for which the Owari-Seki smiths are noted). His naginata and yari are large and dignified, the boshi at times pointed and Jizo-like; the sources credit him as 「短刀, 薙刀の名手として名高い」[[c:3]] (famed as an outstanding maker of tanto and naginata), while noting that the very finest among the naginata are few.

What sets him apart within Owari shinto is exactly what the judges name. His suguha hand, with its fraying habuchi, bright nioiguchi and masame-flowing ji-nie, is the constant by which his tanto are known, and his wet temper marks the Mino-into-Owari Seki descent that the other Owari founders share. On one wakizashi that departs from his usual restraint, bolder in temper and brighter in nie with an antique flavour in the jigane, the published sources judge that he was reaching higher still, 「相州上工, 就中貞宗や信国あたりを狙ったものであろうか」[[c:4]] (aiming, it would seem, at the superior Soshu craftsmen, especially such masters as Sadamune and Nobukuni), and call the result 「同作中出色の一口」[[c:5]] (an outstanding example among his works). His line continued through the second-generation Mino no Kami Fujiwara Masatsune, an adopted son and son of Gifu Daido, whose signed katana and yari survive in the same record.

For the collector, Masatsune is a well-documented founder of an Owari line rather than a rare ghost. Fujishiro grades him Jo saku. He has no National Treasures and no Important Cultural Properties; his record runs instead through the modern Juyo rank, with seventeen blades in the Tokubetsu Juyo and Juyo tiers, and two further pieces designated in the prewar Juyo Bijutsuhin, among them a katana that passed through the Tokugawa Iesato collection and is now held by the Tokugawa Reimeikai Foundation. Provenance touches the daimyo and court houses, with recorded denrai to the Tokugawa family and the Imperial family, and one blade preserved at Akihasan Hongu Akiha Shrine. Because the published sources are agreed that 「刀及び鎬造の脇指は極めて少ない」[[c:6]] (katana and shinogi-zukuri wakizashi are extremely few), a signed katana is the scarce thing, valued as material for the study of the smith himself; his hira-zukuri tanto, wakizashi, yari and naginata come to the serious collector from time to time, and a signed Owari Masatsune of his own hand, not the second generation, remains a satisfying and reachable document of how Owari shinto began.

Masatsune was born at Nodo in Mino Province and first signed Kanetsune, a smith of the Seki tradition who carried that Mino root into the new swords of Owari. The published sources follow his career in unusual detail. In Eiroku 10 he set up an independent branch and moved to Komaki village, changing his name to Masatsune around that time; in Tensho 19 he received the court title Sagami no Kami; in Keicho 5 he followed Matsudaira Tadayoshi to Kiyosu, and he became a retained smith of the Owari Tokugawa house. In Keicho 12 he took the tonsure and retired, passing the name Sagami no Kami Masatsune to his son, but when the second generation died suddenly two years later he returned to the forge, and from that time he signed Masatsune Nyudo. He died in Genna 5 at the age of eighty-four. In later generations he was counted among the Owari Sansaku, the three founding smiths of Owari shinto, beside Hoki no Kami Nobutaka and Hida no Kami Ujifusa.

His recognized hand is the bright straight temper of his hira-zukuri tanto and wakizashi, the form in which his surviving work is most numerous. Over a tightly forged ko-itame mixed with mokume, the steel flows toward masame and carries thick ji-nie, with fine chikei entering and, on several pieces, a mizukage-like feature rising diagonally from below the machi. The temper is a chu-suguha, at times a wide suguha, laid in ko-nie, into which small gunome enter with ko-ashi. What separates his suguha from a plain Seki straight temper is the worked habuchi: it frays into hotsure, with nijuba, kuichigai-ba and uchinoke mixed in and fine sunagashi running through, while the nioiguchi stays bright. The published commentary calls one such tanto a thoroughly characteristic example, with 「相模守政常の典型的な直刃の作例」[[c:1]] (a typical example of Sagami no Kami Masatsune's suguha).

The jigane is the constant beneath both of his manners. It is an itame that overall tends toward masame, with ji-nie attached and, on the better tanto, chikei standing out and the steel reading bright. Where the forging tightens into ko-itame mixed with mokume the impression is of strength, and the published sources single out the diagonal mizukage at the machi and the abundant ji-nie as the marks of his sound forging. On the wakizashi the grain at times stands a little, with the upper half flowing toward the mune, and the carvings he favours, a suken or bonji above the koshimoto with gomabashi on the reverse, are described as crisp and well harmonised with the blade.

His second manner is the Owari-Seki wet temper, carried on his katana, naginata and yari. Over an itame that flows into masame with ji-nie, he tempers a wide suguha tone or a shallow notare-gunome base with togariba and small gunome mixed in, ashi and yo entering, the nie sometimes coarse and gathered in clusters, kinsuji and sunagashi seen, and the nioiguchi tending to a subdued shizumi. The published sources name this directly: on his large Keicho-form katana they read 「尾張関得意の濡れ刃」[[c:2]] (the wet temper for which the Owari-Seki smiths are noted). His naginata and yari are large and dignified, the boshi at times pointed and Jizo-like; the sources credit him as 「短刀, 薙刀の名手として名高い」[[c:3]] (famed as an outstanding maker of tanto and naginata), while noting that the very finest among the naginata are few.

What sets him apart within Owari shinto is exactly what the judges name. His suguha hand, with its fraying habuchi, bright nioiguchi and masame-flowing ji-nie, is the constant by which his tanto are known, and his wet temper marks the Mino-into-Owari Seki descent that the other Owari founders share. On one wakizashi that departs from his usual restraint, bolder in temper and brighter in nie with an antique flavour in the jigane, the published sources judge that he was reaching higher still, 「相州上工, 就中貞宗や信国あたりを狙ったものであろうか」[[c:4]] (aiming, it would seem, at the superior Soshu craftsmen, especially such masters as Sadamune and Nobukuni), and call the result 「同作中出色の一口」[[c:5]] (an outstanding example among his works). His line continued through the second-generation Mino no Kami Fujiwara Masatsune, an adopted son and son of Gifu Daido, whose signed katana and yari survive in the same record.

For the collector, Masatsune is a well-documented founder of an Owari line rather than a rare ghost. Fujishiro grades him Jo saku. He has no National Treasures and no Important Cultural Properties; his record runs instead through the modern Juyo rank, with seventeen blades in the Tokubetsu Juyo and Juyo tiers, and two further pieces designated in the prewar Juyo Bijutsuhin, among them a katana that passed through the Tokugawa Iesato collection and is now held by the Tokugawa Reimeikai Foundation. Provenance touches the daimyo and court houses, with recorded denrai to the Tokugawa family and the Imperial family, and one blade preserved at Akihasan Hongu Akiha Shrine. Because the published sources are agreed that 「刀及び鎬造の脇指は極めて少ない」[[c:6]] (katana and shinogi-zukuri wakizashi are extremely few), a signed katana is the scarce thing, valued as material for the study of the smith himself; his hira-zukuri tanto, wakizashi, yari and naginata come to the serious collector from time to time, and a signed Owari Masatsune of his own hand, not the second generation, remains a satisfying and reachable document of how Owari shinto began.