Tachi〈Inscribed in the West of Aki Province/Leap October Day

Tachi Inscribed "Aki no Kuni Nyūsai / Einin 5, Intercalary 10th Month" — A 1297 Masterwork by the Founding Smith of Aki Sword-Making

Among the long swords (tachi) of late Kamakura-period Japan, a small number bear inscriptions so specific that they read like dated certificates of artistry. This Important Cultural Property — a tachi inscribed "安芸国入西／永仁五年閏十月日" (Aki no Kuni Nyūsai / 5th year of Einin, intercalary 10th month) — is one such treasure. It was forged in the autumn of 1297 by Nyūsai, a swordsmith remembered today as the earliest dated maker of the Aki Province (modern Hiroshima Prefecture) and a key link in the lineage that would eventually produce the legendary Samonji school of Chikuzen.

The blade is privately owned in Tokyo and is therefore not on public display. Yet its very existence — together with a sister sword from two years earlier in the collection of the Japan Sword Museum Technology Research Foundation — anchors the genealogy of medieval Japanese sword-making to a precise place and date, making it a touchstone for scholars and connoisseurs around the world.

The Smith: Nyūsai and the Kyushu Classical Lineage

Nyūsai (入西) was originally a hōshi-kaji — a "priest-smith" who had taken Buddhist orders while continuing to forge blades. He worked in Chikuzen Province (the northern part of modern Fukuoka), one of the most important sword-making regions of medieval Kyushu. According to old swordsmithing genealogies, he was the son or younger brother of Ryōsai (良西), the smith long credited as the founder of the Chikuzen tradition.

The line that flows from him is one of the most celebrated in all of Japanese sword history. The classical pedigree runs Ryōsai → Nyūsai → Sairen (西蓮) → Jitsua (実阿) → Samonji / Ōsa (左文字／大左). Samonji, the great-grandson at the end of this chain, would establish the Sa school in Hakata and pass into legend as one of the foremost swordsmiths of the Nanboku-chō period. To hold a dated work by Nyūsai is therefore to stand at the headwaters of that entire tradition.

Sometime during the Einin era (1293–1299), Nyūsai left Chikuzen and crossed the Inland Sea to settle in Aki Province. The reasons can only be guessed at — Aki was at that time becoming an active military and commercial frontier — but his presence there is the earliest documented case of a master smith working in the area. The Edo-period reference work "Kotō Mei-zukushi Taizen" (古刀銘尽大全, 1792) names him as the oldest swordsmith of Aki Province in the historical record.

Einin 5, Intercalary 10th Month — A Year of Crisis

The date carved into the tang of this tachi places it in the autumn of 1297. To Japanese ears, "Einin 5" carries weighty associations. It was the year the Kamakura shogunate, struggling with the long aftermath of the two Mongol invasions of 1274 and 1281, issued the Einin Tokuseirei — a debt-forgiveness edict intended to rescue impoverished gokenin warriors. The country was anxious, the warrior class was financially squeezed, and the appetite for well-made blades remained intense.

"Intercalary 10th month" (閏十月) is itself a clue. The traditional lunisolar calendar inserted a leap month every few years to keep the seasons aligned, and Einin 5 had a second tenth month after the first. A blade dated to such a month is rare on its face, and the precision of the inscription suggests the smith was aware that he was creating something for which the date would matter — perhaps a votive offering, perhaps a commission for a patron of standing.

Why It Was Designated an Important Cultural Property

The grounds for cultural property designation rest on three pillars: artistic merit, historical significance, and rarity. This tachi answers all three.

Artistically, it is a fine example of late Kamakura craftsmanship in the Kyushu classical idiom — its construction, hamon, and forging style document a southern-school sensibility at a moment of geographic transplantation. Historically, it is one of just two known surviving dated works by Nyūsai (the other, dated Einin 3, that is, 1295, is held by the Japan Sword Museum Technology Research Foundation). Together these two blades are the documentary anchor for a swordsmith whose career would otherwise survive only as a name in old chronicles.

Rarity, finally, is decisive. Dated tachi from the late thirteenth century are uncommon in any school; dated tachi from the founding generation of an entire provincial tradition are rarer still. This blade is the elder of the only two firmly dated witnesses to Aki Province sword-making in the Kamakura era.

Highlights to Appreciate

Even when a sword cannot be viewed in person, understanding what its admirers prize gives the work depth. Connoisseurs of Kyushu classical work look first at the jigane — the surface pattern of the blade. The school's signature is a dark, somewhat coarse itame (wood-grain) hada with strong chikei (inky lines weaving through the steel), giving the surface a wet, almost painterly quality.

The hamon — the tempered edge pattern — in works of this lineage tends toward suguha (a straight line) softened by gentle undulations, with nie (martensite crystals) giving the edge a quiet luminosity rather than the dramatic flamboyance of the contemporary Bizen tradition. Kinsuji and sunagashi — fine streaks of light running through the temper line — are characteristic.

And then there is the inscription itself. The smith's signature on the tang, identifying himself as a maker of Aki Province and dating the work to a specific intercalary month of a specific year, is the kind of epigraphic certainty that scholars of Japanese metalwork rarely encounter. For sword historians, the tang is in some sense the most important surface of all.

Visiting and Related Sights in Tokyo

Because this tachi is in private hands, it is not open to public view. Visitors interested in the world it came from, however, are well served by Tokyo's exceptional concentration of sword-related institutions.

The Japanese Sword Museum (Tōken Hakubutsukan), located within the historic Kyū-Yasuda Garden in Ryōgoku, is the natural starting point. Run by the Society for the Preservation of Japanese Art Swords, it holds National Treasure tachi by smiths from the same era and offers rotating exhibitions that frequently feature Kamakura-period works. The museum is a seven-minute walk from JR Ryōgoku Station and is open from 9:30 to 17:00, closed Mondays.

The Tokyo National Museum in Ueno Park houses one of the world's finest collections of designated sword cultural properties, including National Treasure works by Yasutsuna, Rai Kunitoshi, and other masters of the period. The Honkan (Japanese Gallery) typically devotes a dedicated room to swords with detailed bilingual signage.

For those drawn deeper into the lineage that Nyūsai helped found, exhibitions at the Kyushu National Museum in Dazaifu and at private museums such as the Seikadō Bunko Art Museum periodically display works by his descendants, including the great Samonji himself.