Born in Kyōwa 3 (1803) at Shirakawa in Ōshū, Koyama Munetsugu (固山宗次) carried a smith's name read variously in the as Munobei or Sōbei, working under the art-names Issensai and Seiryōsai. He came up alongside elder brothers Munehira and Munetoshi, and although his teacher is traditionally given as Katō Tsunahide, the readers repeatedly note that the hand of Katō Tsunatoshi shows through his work more plainly. He first served the Matsudaira house of Shirakawa as a retained smith; when that domain was transferred to Kuwana in , he settled in at Azabu Nagasaka and forged as a Kuwana domain smith. In Kōka 2 (1845) he received the court title no , the signature no Fujiwara Munetsugu recurring on the dated from that point. His production runs from the latter half of Bunsei into the early Meiji years, and the program it serves is the Bakumatsu fukko revival of -: a deliberate return, from an workshop, to the tempering of the old masters.
The shared idiom is consistent across the line. Construction tends to a wide , thick , shallow and an extended or , giving the heavy-in-hand bearing the readers call . The ground is a tightly packed , sometimes flowing toward or , carrying extremely fine -grade and frequent ; faint rises on a number of blades. The temper is the heart of the recognition: a -dominant or gunome-chōji, with , and angular heads mixed in, long and entering, fine and , and a bright, clear . To read his hand, the flag particular shapes (the tadpole-head and the kobushi fist-shaped clustered near Keiō-dated work), a turning in with , and the bold, thick-chiseled signatures with prominent chisel-pillows. Cutting-test inscriptions are common, several tied to the connoisseur Iga Norishige, who is recorded learning swordmaking from Munetsugu. His pupils carry the vocabulary: Tairyūsai Sōkan (宗寛, also Munekane), son of Ōno Heizō and later a /Furukawa domain smith, whose blades add a faint and a smaller-pattern late temper; and the likely student Kongōsai Munehiro, who copied the shrine original his master did.
For , the discriminating points are the orderly yet varied arrayed shoulder-to-shoulder, the -laden Tenpō-era pieces whose has not yet settled, and a deliberate allusion to the second-generation Kunisuke when kobushi-like appear. The named works root the line in documented copying: an of the National Treasure Koryū Kagemitsu, reconstructed to its original state with and carved by Sōkan; and a Tenpō 11 (1840) copying the hōchō-shaped Masamune of Egara Tenmangū in , carved by Tōryūsai Seiju and dedicated by Nomura Toshikatsu, a rare pairing of two masters. Provenance inscriptions name patrons such as Miyake Takuma and the Furukawa domain on the Sōkan side. Across the register, the work stands as a disciplined restatement of the tradition, prized for the brightness of its and for the documentary value of its dated, commissioned and trial-cut tangs.