Ōdachi Attributed to Bungo Tomoyuki: A National Treasure of Extraordinary Scale

Among the countless masterworks of Japanese sword-making that have survived the centuries, few can rival the sheer awe inspired by the Ōdachi (great sword) attributed to the Bungo swordsmith Tomoyuki. Designated a National Treasure of Japan, this unsigned blade resides at Oyamazumi Shrine on Omishima Island in Ehime Prefecture—an institution often called the "Island of National Treasures" for its unparalleled collection of arms and armor. With an overall length of approximately 275 cm and a blade length of 180 cm, this extraordinary weapon stands taller than virtually any person who might behold it, offering a visceral connection to the warrior culture of the Nanbokuchō period (1336–1392).

What Is an Ōdachi?

An ōdachi, also known as a nodachi (field sword), is a category of Japanese long sword characterized by a blade length exceeding approximately 90 cm (about 3 shaku). These oversized weapons rose to prominence during the late Kamakura and Nanbokuchō periods, when mounted combat and bold, sweeping attacks on the battlefield demanded ever-larger blades. Unlike the more common tachi or katana, ōdachi were typically carried slung across the back or borne by an attendant, owing to their great length. Their production required extraordinary skill, as forging a blade of such scale without structural flaws was a considerable technical challenge.

The Nanbokuchō period, marked by the conflict between the Northern and Southern Courts, saw the peak of ōdachi popularity. Warriors on both sides of the struggle favored these imposing swords as symbols of martial prowess and as practical weapons for horseback combat, where the extended reach could prove decisive.

The Sword Itself: Dimensions and Craftsmanship

The National Treasure ōdachi attributed to Tomoyuki is a truly remarkable piece of sword-making. Its key physical characteristics demonstrate the pinnacle of Nanbokuchō-period craftsmanship:

• Overall length: approximately 275 cm
• Blade length (nagasa): approximately 180 cm
• Curvature (sori): approximately 5.4 cm
• Construction: shinogi-zukuri (ridgeline construction) with a bo-hi (single groove) running along the blade

The steel shows an ō-itame-hada (large wood-grain pattern) with a flowing texture, while the hamon (temper line) features ko-midare (small irregular pattern) mixed with gunome (zigzag undulations). The blade retains its original, unshortened tang (ubu-nakago), which is exceptionally rare for a sword of this age and size—most ōdachi were later shortened (suriage) for practical use. The fact that this blade has survived fully intact speaks to its status as a treasured ceremonial and votive object rather than an everyday weapon.

Though the blade bears no signature, analysis of the steel quality and forging style has led experts to attribute it to the Bungo swordsmith Tomoyuki, considered the founder of the Ko-Takada (Old Takada) school of sword-making in what is now Ōita Prefecture. Tomoyuki is traditionally regarded as a disciple of the Samonji lineage, one of the most respected sword-making traditions of the era.

The Legend of Ōmori Hikoshichi and the Battle of Minatogawa

The history of this ōdachi is intertwined with one of the most dramatic chapters of medieval Japanese history. According to tradition, the sword was the personal weapon of Ōmori Hikoshichi (Ōmori Morinaga), a warrior who fought on the side of Ashikaga Takauji during the pivotal Battle of Minatogawa in 1336. In this decisive engagement, the forces loyal to the Ashikaga shōgunate clashed with the Southern Court loyalists led by the legendary Kusunoki Masashige. Ōmori Hikoshichi is said to have been the warrior who struck down Kusunoki Masashige—one of the most revered figures in Japanese military history, celebrated for his unwavering loyalty to Emperor Go-Daigo.

The sword's connection to this famous battle lends it an aura of profound historical significance. In 1470, Ōmori Naoji, a grandson of Hikoshichi, donated this ōdachi along with three tan (approximately 0.3 hectares) of rice paddy land to Oyamazumi Shrine. Together with the sword, Naoji also offered the original nodachi-koshirae (field-sword mounting), which has been designated as a National Treasure accessory (tsuki). This mounting features a leather-wrapped hilt with black lacquer in a stone-grain pattern, a scabbard covered in double layers of thin leather and amber-colored leather over black lacquer, and a guard made of layered molded leather with gilt-bronze edging.

Why Was This Sword Designated a National Treasure?

The ōdachi attributed to Tomoyuki was first designated an Important Cultural Property on March 27, 1901, and elevated to National Treasure status on February 8, 1958. Several factors contributed to this distinguished recognition:

• Exceptional scale: At 180 cm in blade length, it is one of the longest surviving ōdachi in Japan, demonstrating the technical mastery required to forge such a weapon without structural failure.
• Outstanding preservation: The retention of the original unshortened tang is extremely rare among swords of this era, providing invaluable information about Nanbokuchō-period sword-making techniques.
• Historical provenance: Its association with Ōmori Hikoshichi and the Battle of Minatogawa connects the sword to a defining moment in Japanese history.
• Complete mounting: The survival of the original nodachi-koshirae together with the blade is exceptionally uncommon and offers a complete picture of how such a weapon was carried and used.
• Artistic quality: The sophisticated metallurgical work, including the flowing itame grain and complex hamon pattern, represents the finest achievements of the Ko-Takada school.

Oyamazumi Shrine: The Island of National Treasures

Oyamazumi Shrine (大山祇神社), situated on Omishima Island in the Seto Inland Sea, is one of Japan's most historically significant shrines. Enshrining Ōyamatsumi-no-Kami—a deity revered as the god of mountains, seas, and warfare—the shrine has attracted the devotion of warriors, naval commanders, and imperial courts since ancient times. Its origins are said to date back to the reign of Emperor Nintoku, making it one of the oldest religious sites in the Shikoku region.

As the head shrine of all Yamazumi and Mishima shrines across Japan, Oyamazumi Shrine accumulated an extraordinary collection of arms and armor through centuries of votive offerings by grateful warriors. Today, the shrine's treasure halls house eight National Treasures and over 470 Important Cultural Properties—including approximately 40% of all nationally designated armor and helmets in Japan. Among its most celebrated holdings are suits of armor attributed to Minamoto no Yoritomo and Minamoto no Yoshitsune, the oldest surviving ō-yoroi (great armor) in Japan, and a Tang Dynasty bronze mirror designated as a National Treasure.

The shrine grounds themselves are a natural monument, with 38 ancient camphor trees designated as a national Natural Monument. The largest of these is believed to be approximately 2,600 years old, creating an atmosphere of timeless sanctity.

Visiting the Treasure Hall

The ōdachi attributed to Tomoyuki is displayed in the shrine's treasure hall complex, which consists of the Shiyōden (紫陽殿) and the National Treasure Hall (国宝館). All eight National Treasures in the shrine's collection are, in principle, on permanent display, allowing visitors to view them at any time during opening hours. Photography within the treasure halls is prohibited, so visitors are encouraged to take their time and appreciate these masterworks with their own eyes.

Standing before this enormous blade, visitors can feel the weight of history and the martial spirit of the Nanbokuchō period. The sheer physical presence of the sword—taller than most people—is difficult to convey in photographs or words. It is an experience best savored in person.

Surrounding Attractions and Travel Tips

Omishima Island offers much more than the shrine alone. The Shimanami Kaido, one of Japan's most celebrated cycling routes, connects the island to both Hiroshima Prefecture and the city of Imabari in Ehime Prefecture via a series of spectacular bridges spanning the Seto Inland Sea. The area is also known for its citrus orchards, fresh seafood, and relaxing hot spring facilities such as Maré Grassia Ōmishima, a marine spa with panoramic views of the sea.

A short walk from the shrine, the roadside station "Shimanami no Eki Mishima" offers local produce, souvenirs, and light meals featuring regional specialties. The island's quiet rural atmosphere and stunning coastal scenery make it an ideal destination for travelers seeking a more contemplative and authentic experience of Japanese culture, far from the crowds of major tourist centers.