Yamato province, with Nara at its heart, held the oldest continuous tradition of swordmaking in Japan, and the blades grouped here as Ko-Yamato reach back to a horizon before the five classical schools of the (Senjuin, , Shikkake, , Hosho) had separated into distinct lines. The place these works in the period, with several appraised as not descending later than the late or early , and one judged no later than . At the far root stands Amakuni (天国), to whom the imperial Kogarasu- (小烏丸) is attributed; that blade, a - form, is read as early- work predating curved swords, an ancient type whose forging is said to continue methods seen in the Shōsōin treasures. The remaining pieces are unsigned and carry only collective registers such as Yamato smiths (大和鍛冶) and Yamato ko- (大和古剣). Their temple context is explicit: Yamato held the great monasteries beginning with Tōdaiji and Kōfukuji, and the note that , carried by Buddhist clergy for rites rather than by warriors, would naturally have issued from this province in greater number than elsewhere.
Across the unsigned blades a consistent vocabulary emerges. The construction is ryō-shinogi-zukuri with a high and archaic proportions, the not swelling and the point area restrained; one blade is thought to have begun as the inner blade of a . The tends to , often with one face forged in and the other in flowing , the texture viscid and carrying thick , , -like mottling, and conspicuous . The is -based with a shallow , the showing vigorous , , , uchi-noke, and , with and through coarse-tending ; the inclines to . The is finished with , and several blades carry -otoshi, the temper dropped above the base so that only the upper portion is hardened. These traits, more than any single feature, mark the archaic Yamato character before the schools differentiated.
For , the combination reads as Yamato at its oldest: the ryō-shinogi-zukuri form, the -tending ground with strong and , the -otoshi and finish, and the worked with and . The observe that by their nature reveal the individual maker less readily than , so these works rest at the school level rather than under a personal name; only Amakuni is held by tradition. Yet the ground, with frayed , and -otoshi foreshadow the later five schools, which preserved and refined this inheritance. The named provenance is weighty: Kogarasu- passed as a treasure of the Taira clan, said to have been brought to Emperor Kanmu by a divine crow of Grand Shrine and later bestowed on Taira no Sadamori, and it remains in the Imperial collection. The unsigned , by contrast, document the workshop tradition itself, the ancient Nara forging that the would carry forward.