Tachi〈Inscribed on November 1st, 1st Year of Bishu Osafune

Tachi Signed by Osafune Masamitsu, Dated 1361

In the eleventh month of the first year of the Kōan era, which corresponds to 1361, a swordsmith working in the riverside village of Osafune in Bizen Province cut his name and the date into the tang of a long blade. The inscription reads "Bishū Osafune Masamitsu," followed by the year. Among the dated works that survive from this maker, none is older. The blade is now kept at the Tokyo National Museum in Ueno, an Important Cultural Property that marks the beginning of a career documented across some four decades.

What makes the piece quietly compelling is not a famous nickname or a story of a celebrated owner. It is the date itself. A signed and dated tachi from the Nanbokuchō period, made by a smith of the most influential workshop of its age, gives historians a fixed point against which other, undated works can be measured.

The Maker and the Osafune Workshop

Osafune, in what is now Setouchi City in Okayama Prefecture, grew up along the lower Yoshii River, a region rich in the iron sand that sword forging demanded. By the late Kamakura and Nanbokuchō periods the workshops here had become the largest and most productive in Japan. The lineage usually given runs from Mitsutada, regarded as the effective founder, through Nagamitsu, Kagemitsu, and then Kanemitsu, the smith who led Osafune into the turbulent fourteenth century.

Masamitsu belongs to this circle. He is recorded by tradition as a son of Kanemitsu, and his work follows closely on his teacher's. The fourteenth century was an age of near constant fighting. The court had split into rival northern and southern lines in 1336, and the warfare of the following decades shaped what swordsmiths produced, favouring broad, powerful blades. Kanemitsu had absorbed ideas from the Sōshū tradition of Sagami Province, blending them with the older Bizen manner to create what later connoisseurs called Sōden-Bizen, a Bizen style carrying Sōshū influence. Masamitsu inherited this approach.

According to studies of his surviving dated blades, Masamitsu worked over roughly forty years, with this 1361 tachi standing at the early end and pieces from the Ōei era of the early 1400s at the later end. That span makes the museum's blade a useful anchor for placing the rest of his output in sequence.

Why It Is Designated

The sword was recognised as an Important Cultural Property on 29 August 1950, the day the Cultural Properties Protection Law came into force and a large group of works entered the national registers together. Its value rests on several plain facts rather than on legend.

First, it carries a full date inscription. Many old blades are unsigned, or had their signatures lost when the tang was shortened to fit later mounts. A tachi that still bears both the maker's name and a precise year is comparatively rare, and rarer still when the tang survives in its original, unshortened form. Second, it is the oldest dated work known from Masamitsu, which gives it a documentary weight beyond its appearance. Third, it shows the Sōden-Bizen manner of the Osafune school at a specific moment, allowing the style to be tied to a date rather than estimated.

Records in the national cultural-properties database do not publish the blade's measurements, and the museum does not list it among works on permanent view. The piece is best understood through its inscription and its place in Masamitsu's chronology.

What to Look For

Anyone who has the chance to see the blade in person should begin where the smith began, at the tang. The characters of the signature and the date are the heart of the object, the part that turns an anonymous antique weapon into a dated historical document. Reading right to left along the tang, the name comes first and the year follows.

The forging itself reflects Bizen practice of the period. Blades from this circle typically show a wood-grain pattern in the steel, called itame, with an undulating temper line, or hamon, of the kind Kanemitsu favoured in his later years. Because Masamitsu followed his teacher so closely, his work can be hard to separate from Kanemitsu's at a glance, which is part of why a securely dated, signed example matters so much. Japanese swords reward slow looking under raking light, where the grain of the steel and the activity within the temper line come alive.

Seeing It in Tokyo

The blade is held at the Tokyo National Museum, the country's oldest and largest museum, set within Ueno Park. Swords there are displayed in the Japanese gallery of the main building, the Honkan, in a dedicated room, and the selection rotates every few months to protect the blades from prolonged exposure. This particular tachi is not on permanent display, so anyone hoping to see it should check the museum's current exhibition listings before travelling.

Even when it is in storage, the museum's sword room is among the finest places in the world to understand Bizen work. The collection includes celebrated Osafune blades, among them the National Treasures known as Daihannya Nagamitsu and Kogarasu, alongside the famous Mikazuki Munechika, which appear in rotation. Seeing several together makes the family resemblance of the Osafune smiths, and the small differences between them, far easier to grasp.

Ueno Park itself rewards a full day. The surrounding grounds hold several major museums, a noted zoo, and, in spring, some of the most visited cherry blossoms in the city. The museum sits a short walk from Ueno Station, served by the JR lines and the Tokyo Metro.