AS25507 Katana：Mumei (attributed to Ko-Naminohira) (41st NBTHK Juyo Token)

Ordering number:AS25507

Katana in Shirasaya (41st NBTHK Juyo Token)

Signature: Mumei (attributed to Ko-Naminohira)
無銘(古波平)

We divide 4 sections for each sword as Saijyo Saku, Jyojyo Saku, Jyo Saku and Regular Saku.
This blade is ranked as Saijyo Saku (the highest level) among works attributed to Mumei (Ko-Naminohira).
Habaki: Gold foiled single Habaki.
Blade Length: 76.6 cm (30.16 in)
Curvature: 2.5 cm (0.98 in)
Mekugi Hole: 2
Width at Base (Motohaba): 3.01 cm (1.18 in)
Width at Tip: 1.78 cm (0.70 in)
Thickness of rim (Kasane): 0.62 cm (0.24 in)
Sword Weight: 855 g
Shape: This blade remains close to its original length, with a deep curvature.
Jigane: The Hamon on the shinogi-ji and that on the main body appear identical.
Hamon: The Hamon typical of the Kamakura period is vivid and clear, and the Boshi shows the same characteristics.

Features: Ko-Naminohira swords were highly favored by naval officers because the name “Naminohira” (literally “flat waves”) symbolized calm seas. These swords originated in Naminohira, Taniyama-go, Taniyama District, Satsuma Province — present-day Kamihabamoto, Kagoshima City, Kagoshima Prefecture.
During the Battle of Ichinotani, a warrior named Ibo Noritsuna, known for his unmatched strength, used a blade crafted by Naminohira of Satsuma Province to take the head of Etchu-no-kami Moritoshi. The nearby coastline of Naminohira was known to be rich in iron sand, making it an ideal place for swordsmithing.
Among existing works, the swordsmith Yukiyasu is considered the founder of this lineage. The Naminohira school is generally categorized into different periods: Kotō (Old Sword period), Ko-Naminohira (Old Naminohira), Chu-Naminohira (Middle Naminohira), and Sue-Naminohira (Late Naminohira). The earliest Naminohira smiths are believed to have been active during the Heian period, including Yukiyasu, Yukihito, Yasunori, Yukimasa, and Yasumitsu.

Aoi Art’s Comment: This tachi measures 76.6 cm in length and is nearly ubu (unaltered), showing a grand and elegant appearance.
It was exhibited at the Japanese Sword and Tosogu Exhibition hosted by the Oita Branch of the NBTHK in 1998 (Heisei 10).
The sword is recorded in important reference books as a Kamakura period piece.
It is a magnificent and dignified work, featuring a bright and clear suguba hamon characteristic of Ko-Naminohira.
The yasurime (file marks) on the tang are still visible.
Although designated as a Kamakura-period blade in sword references, it may date back even earlier.
Discovered in Kagoshima, this piece has an elegant form with no flaws or defects on the blade—an exceptional work to be treasured at home.
According to the Japanese Sword Museum, a swordsmith named Masakuni migrated from Yamato to Naminohira around the Eien era of the Heian period, becoming the school’s founder.
His son, known as Yukiyasu, continued the line, which lasted well into the modern period.
“Ko-Naminohira” refers to works no later than the Nanbokucho period.
Their style closely resembles the Yamato tradition, but their ji-hada and ha show distinctive characteristics: the nioiguchi is soft and moist, the jihada has a sticky texture, and the yakiba sometimes ends in yakiotoshi near the tang.
This sword, although unsigned and suriage (shortened from the tang), retains a koshi-zori curvature, with a slender form, high shinogi, and clear difference in width between base and tip.
While the overall style suggests Yamato-den, close inspection reveals a resemblance to Yamato proper, but with a more sticky, shiroke utsuri (pale reflection), soft and moist nioiguchi, and subtle irregularities in the suguha hamon—traits that identify it as Ko-Naminohira.
Based on its characteristics, this is considered an excellent piece from a school that predates the Kamakura period.

41st NBTHK Juyo Token
Aoi Art estimation paper
Whole Oshigata included