Tachi Signed Rai Kunitsoshi: A National Treasure of Japanese Swordsmithing

Among the roughly 110 swords designated as National Treasures of Japan, the tachi bearing the signature of Rai Kunitsoshi (来国俊) holds a special place. Forged during the late Kamakura period—an era when Japan's swordmaking arts reached extraordinary heights—this blade is an exceptional example of the celebrated Rai school's craftsmanship. What makes it particularly remarkable is that it represents a rare departure from the swordsmith's signature style: a masterful display of midare-ba (irregular temper line) from an artisan renowned for his refined suguha (straight temper line) work.

The Rai School: Kyoto's Premier Sword-Forging Lineage

The Rai school (来派) was one of the most distinguished swordsmithing lineages in Japanese history. Active from the mid-Kamakura period through the Nanbokuchō era, the school was based in Yamashiro Province—present-day Kyoto—the imperial capital and cultural heart of Japan. According to the medieval text Meizukushi (Kanchi-in manuscript), the Rai school's ancestors were said to have come from the Korean peninsula, and the prefix "Rai" (来, meaning "to come") in their name may reflect this tradition.

The practical founder of the school was Rai Kuniyuki (来国行), who established the workshop's distinctive approach: blades of gentle, graceful form with immaculate forging. His son—or, according to some scholars, grandson—Rai Kunitsoshi carried the school to even greater prominence. From Kunitsoshi onward, the Rai school became the foremost swordsmithing group in Yamashiro Province, eventually superseding the earlier Awataguchi school.

Kunitsoshi was active from approximately 1278 to 1321, with a documented inscription on one work noting his age as seventy-five years old in 1316. His prolific career produced both tachi (long swords) and tantō (daggers), and multiple works by him have been designated as National Treasures. He is widely regarded as one of the greatest swordsmiths of the Yamashiro tradition.

A Question of Identity: Niji-Kunitoshi and Rai Kunitsoshi

An intriguing scholarly debate surrounds the Kunitoshi name. Some blades bear only the two-character signature "Kunitoshi" (国俊), while others carry the three-character inscription "Rai Kunitsoshi" (来国俊). These two groups of works differ substantially in style: the two-character blades tend to be bold and powerful with large chōji-midare (clove-shaped irregular) temper patterns, while the three-character blades are typically more refined, featuring slender forms and elegant straight temper lines.

This stylistic contrast has fueled a long-running debate over whether the two-character and three-character signatures represent the same individual at different career stages, or two separate swordsmiths. The prevailing theory suggests they were different people—possibly father and son—with the two-character Kunitoshi (often called "Niji-Kunitoshi") being the elder. The National Treasure tachi discussed here bears the three-character "Rai Kunitsoshi" signature and is attributed to the later of these master swordsmiths.

Masterful Construction: The Blade in Detail

This tachi is constructed in the shinogi-zukuri style with an iori-mune (ridged back), featuring a graceful koshi-zori (curvature centered at the base) with funbari (tapering at the base of the blade). The kissaki (point) is small and elegant, contributing to an overall silhouette of refined beauty.

The forging—or jihada—is a hallmark of the Rai school's meticulous craftsmanship. The steel shows ko-itame hada (fine, tightly packed wood-grain pattern) with ji-nie (crystalline particles visible in the body of the blade) and nie-utsuri (a cloudy reflection effect in the steel). This combination creates a surface of exceptional refinement and depth.

What truly sets this blade apart is its hamon (temper line). While Rai Kunitsoshi was celebrated for his mastery of suguha—the straight, disciplined temper line that became his trademark—this tachi reveals his ability to create exquisite midare-ba as well. The hamon consists of fine suguha with ko-chōji (small clove-shaped irregularities) mixed in. At the middle section of the blade, the pattern becomes slightly more flamboyant, and on both sides, subtle koshiba-style patterns appear. The overall nioi-guchi (boundary of the temper line) is tight and precise, accented with ko-nie.

The tang (nakago) is in its original, unaltered state—known as ubu—which is exceptionally rare for a blade of this age. It features a chestnut-shaped tip, shallow katte-sagari file marks, a single mekugi-ana (peg hole), and the three-character signature placed just below the habaki (blade collar).

Why This Blade Became a National Treasure

This tachi was first designated as an Important Cultural Property on July 3, 1941, and then elevated to National Treasure status on November 22, 1952, under Japan's Law for the Protection of Cultural Properties. Several factors contributed to this prestigious designation.

First, it is a rare example of Rai Kunitsoshi's midare-ba work. While most surviving blades by this smith feature his signature straight temper line, this tachi demonstrates his exceptional versatility. Experts have described it as a masterpiece of irregular tempering—skillfully calculated and perfectly executed, with the refined forging providing an ideal canvas for the dynamic temper pattern.

Second, the signature style closely matches that found on a documented work dated to 1290 (Shōō 3), placing this blade in Kunitsoshi's early career period—around the Shōō to Einin eras (approximately 1288–1298). This makes it valuable not only as a work of art but also as historical evidence for understanding the smith's stylistic development.

Third, the preservation of the original tang in its unaltered state is remarkable for a blade over seven hundred years old. Many tachi from this period were later shortened (suriage) to serve as katana during the Muromachi and later periods. That this blade retains its original form adds immeasurably to its historical and artistic significance.

Historical Provenance: From Feudal Retainers to National Treasure

This tachi has been passed down through the Kan family (菅家), who served as senior retainers (karō) of the Shōnai domain in present-day Yamagata Prefecture. The Shōnai domain was ruled by the Sakai clan throughout the Edo period, and the Kan family held prominent positions within the domain's administration.

That such a prestigious blade was held by a domain retainer family—rather than the ruling lord—speaks to the high status and wealth of karō families in feudal Japan. The careful preservation of this sword through centuries of the family's stewardship ensured that this remarkable blade survived in exceptional condition to the present day.

Where to Experience Japanese Sword Culture in Tokyo

As this tachi is held in a private collection, it is not on permanent public display. However, privately owned National Treasure swords in Japan are occasionally exhibited at museums and special exhibitions. Sword enthusiasts visiting Tokyo can explore Japanese sword culture at several outstanding institutions.

The Tokyo National Museum in Ueno maintains an extensive collection of swords, with rotating exhibitions in its dedicated sword gallery (Room 13 of the Main Building). Visitors can regularly view National Treasure and Important Cultural Property blades, including works by other Rai school smiths. The museum is easily accessible from Ueno Station on the JR and Metro lines.

The Japanese Sword Museum (Tōken Hakubutsukan) in Sumida Ward, operated by the Society for the Preservation of Japanese Art Swords (NBTHK), is entirely dedicated to Japanese sword culture. Its collection includes National Treasure tachi, and the museum offers English-language resources to help international visitors understand the nuances of blade appreciation.

The Nezu Museum in Minato Ward, Tokyo, also holds sword-related exhibitions and owns a separate Rai Kunitsoshi tachi (classified as an Important Art Object). Its beautiful traditional garden offers a serene complement to the art viewing experience.

Tips for Appreciating a Japanese Sword

For visitors encountering Japanese swords in a museum setting for the first time, understanding a few key elements will greatly enhance the experience. Observe the overall silhouette (sugata) of the blade—its length, curvature, and proportions tell the story of the era in which it was made. Look for the hamon, the temper line that runs along the cutting edge, which reveals the swordsmith's artistic vision. Examine the jihada (forging pattern) on the flat of the blade; like wood grain, it varies from smith to smith and school to school. Finally, study the nakago (tang) and its inscriptions—the smith's signature and sometimes dates provide a direct connection to the creator.

Museums in Japan typically display swords in well-lit cases that allow visitors to observe these features closely. Taking your time with each blade—rather than rushing from case to case—will reward you with a deeper appreciation of these remarkable works of art.