The Fukuoka Ichimonji lineage arose in the early Kamakura period with Norimune as its founder, reaching its greatest prosperity during the mid-Kamakura era. The early craftsmen of this tradition—including Norimune, Sukemune, Narimune, Naomune, Muneyoshi, Munetada, Shigehisa, and Sadazane—are distinguished by the designation "Ko-Ichimonji" (Old Ichimonji). Among the most celebrated Bizen oban-kaji (smiths serving in the imperial guard smithy), these artisans produced works that, while preserving the archaic elegance of their Ko-Bizen predecessors, introduced subtle technical refinements that marked the transition into a more deliberate forging aesthetic.

The collective style of Ko-Ichimonji demonstrates a delicate balance between tradition and innovation. The forging typically displays itame-hada with fine ji-nie, often mixed with mokume, and midare-utsuri appears with vivid clarity—a feature more pronounced than in Ko-Bizen works. The hamon characteristically combines ko-chōji with ko-gunome, ko-notare, and ko-midare, creating small-patterned irregularity rich in nie-based activity. The tempered edge exhibits abundant ko-ashi and yō, with well-adhering ko-nie, and is enlivened by vigorous kinsuji and sunagashi. In many examples, fine tobiyaki resembling yubashiri appears, and the nioi is notably deep. While the nie is not as robust as in Ko-Bizen, the conspicuous presence of ko-chōji and the slightly fresher feeling in the yakiba distinguish these works from their earlier counterparts. Blade construction often retains high koshizori with pronounced funbari and compact ko-kissaki, displaying the dignified proportions typical of early Kamakura tachi. Many works remain in ubu (original unshortened) condition, frequently unsigned—a testament to the period's conventions.

Ko-Ichimonji occupies a pivotal position in the evolution of Bizen craftsmanship, representing a transitional phase between the austere power of Ko-Bizen and the brilliant ornamentation of mid-Kamakura Fukuoka Ichimonji. The group's work does not yet possess the splendid, flamboyant chōji-midare that would define later Ichimonji production, yet demonstrates a more orderly and conspicuous treatment of chōji patterns combined with clearer utsuri. This measured approach, preserving archaic taste while introducing technical nuance, reflects the refinement of an emerging classical aesthetic. The Ko-Ichimonji smiths thus established the foundation upon which the Fukuoka Ichimonji school would build its mid-Kamakura magnificence, making their contribution essential to understanding the development of one of Bizen's most influential lineages.