The school (-) represents one of the two paramount traditions of Province swordmaking during the period, flourishing alongside the lineage from the early thirteenth century through the era. The school's name derives from the practice of carving the character (一, "one") onto the , though signatures varied considerably—some blades bear only this single ideograph, others append an individual maker's name beneath it, and still others carry personal names alone. The tradition prospered across multiple geographic centers within , most notably at Fukuoka during the mid- period, followed by Yoshioka from the late into the era, with additional branches at Katayama and Iwato. Each locale developed its own stylistic nuances while maintaining the school's fundamental aesthetic principles.
The collective technical signature of work centers on brilliant tempering executed with extraordinary virtuosity. The mid- Fukuoka masters in particular forged blades of exceptional flamboyance, tempering large-scale , layered (multi-petaled clove patterns), fukuro-chōji (bag-shaped clove forms), and kawazu-kochōji (frog-leg small clove patterns) that rise and fall dramatically across the blade surface. The characteristically displays vivid (irregular reflection in the steel) standing clearly against an foundation, with densely adhering (martensitic particles in the ground steel) and fine (地景, steel veining). The tempering itself is distinguished by a soft, luminous (hardening boundary) rich in internal activity— and (leg-like and leaf-like crystalline formations) appear in profusion, while and (金筋・砂流し, lightning-like and sand-flow patterns) run frequently through the . The Yoshioka branch, which rose to prominence as Fukuoka's influence waned, typically produced more restrained work with patterns of smaller scale, often incorporating conspicuous (clover-shaped elements) and occasionally showing (reverse-slanting) tendencies. The Katayama group, reportedly founded when the smith Norifusa relocated from Fukuoka, became particularly renowned for (polearms), forging strong, clear steel with somewhat smaller patterns that characteristically lean in reverse, featuring fine, intricate within the temper.
The school's enduring influence stems from its synthesis of technical excellence with aesthetic grandeur. Early works of the tradition often display (small irregular patterns) more prominently than and retain a character, but by the middle period the school had perfected the magnificent for which it became celebrated. These blades preserve the powerful form of their era—deep (curvature concentrated at the base), pronounced (flaring at the base), and well-balanced (flesh or convexity of the blade)—combined with forging of exceptional quality in which both and achieve a bright, (sound and healthy) character. The school's masters succeeded in creating works that unite martial vigor with ornamental brilliance, tempering patterns that alternate between sumptuous, boldly undulating compositions and more controlled arrangements with aligned (temper peaks), combining motion and stillness in a manner that engages the viewer without exhausting the eye. This aesthetic achievement, coupled with the school's technical sophistication in producing dense, fine-textured steel with vivid and richly active tempering, secured 's position as one of the most celebrated and influential sword-forging lineages in Japanese history.