Koyama Munetsugu was born in Kyowa 3 (1803) at Shirakawa in Oshu, common name Sobe, with the art names Issensai and Seiryosai. The published sources record that his teacher is said to have been Kato Tsunahide of Yonezawa, but add that, judging from his manner of work, "the influence of the younger brother Kato Tsunatoshi was rather the greater". He served first the Matsudaira house of Shirakawa, and when that domain was transferred he became a smith for the Kuwana fief in , living in at Azabu Nagasaka. In Koka 2 (1845) he received the title no . He worked from the latter half of the Bunsei era into the early Meiji years, signing as Nishiyama, as Koyama, and as no Fujiwara Munetsugu, and the sources note that his surviving works are extremely numerous. They sum up his career in one phrase: "his style was consistently -".
His characteristic hand is a and in the manner. He sets mixed with , pointed elements, and , with entering long and well, and one entry likens a of his to the manner of Kanemitsu. The temper is -dominant with adhering, and what the published sources return to most often is the : bright and clear on the majority of his blades, and on a number of them described as tight as well. On one Tenpo finished in his showiest vein, the sources write that he has "finished it in a more flamboyantly -dominant than usual", noting in the upper half and a bright .
The is his other constant. His usual is a well-packed , so finely forged that it often looks almost plain, with fine and at times fine . The published sources summarise his success on exactly these two elements together, saying that "over a well-packed, beautiful forging he tempers a -dominant , and succeeds". The runs in to a turnback, at times pointed with . Carving, where present, is a or a paired groove, sometimes with , goma-bashi, or a sacred invocation, and his son Yoshitsugu supplied the carving on some blades.
Besides his mainline he was a deliberate copyist. Of one the published sources say that "this is typical of Munetsugu's copy-work": the takes , especially Yosozaemon no Jo Sukesada, as its model, and the copies the Oei- masters Morimitsu and Yasumitsu, succeeding in producing . A of Tenpo 11 copies the large -shaped blade attributed to Masamune that is a treasure of the Egara shrine in , and was dedicated at the Shiba Shinmei shrine in . A separate vein is the broad, long blades of the Tenpo years, wide in body with a thick , in which the departs from his usual tight grain into an mixed with and flowing grain, standing and with and . The sources say this is often seen in his Tenpo work. A quieter register survives as well but is rare.
His place in the bakumatsu rests on the completeness of his revival and on the documentary richness of his blades. The sources note that he "seems to have been well known as a master of -", and he forged a at the command of the lord of . Many of his blades carry cutting-test inscriptions by the Yamada house, tried at Senju and elsewhere. One was forged at the command of Lord Date Munenari of Uwajima from the ring-iron of a foreign ship, an inscription the sources call "precious also for the history of the bakumatsu". His bright over a near-plain sets his work apart from the deeper, softer of the blades he studied.
For the collector Munetsugu is a signed and abundant master rather than a rarity. Fujishiro grades him Jo-jo . He has no National Treasures and no Important Cultural Properties; his standing on the designation record runs through the rank, where fifty-two of his works are held, all signed, the broad named his typical and representative work. His recorded provenance reaches the lord of and a retainer, Matsudaira Chikanai of the Shonai domain, and Lord Date Munenari of Uwajima. Because so many were made and so many survive, a signed and dated Munetsugu of good workmanship comes to market from time to time, and remains one of the more attainable ways for a collector to hold a documented, cutting-tested bakumatsu - blade.