The Yoshii tradition (Yoshii-) represents a distinctive and independent lineage within the sword-making province, traditionally said to have originated in the late period with the smith Tamenori. Unlike other schools that were absorbed into the dominant mainstream during the period, the Yoshii school maintained its individuality and continued to produce works marked by a recognizable style. The group flourished from approximately the Karyaku era (1326–1329), when dated works by the smith Kagenori—a contemporary of prominent smiths such as Kagemitsu and Chikakage—begin to appear. Works produced through the period are collectively referred to as (Old Yoshii), distinguished from later -period production. Although signed examples from the period itself are exceedingly rare, the school's presence is well documented through both inscribed blades and the considerable body of unsigned works attributed on the basis of technical features.
The collective workmanship of the Yoshii group is characterized by a highly distinctive tempering pattern in which small irregular undulations () appear to link together in continuous, running sequences (). This signature trait distinguishes Yoshii work from the patterns of the tradition, both in form and in execution. examples typically display a foundation of finely adhering martensite particles (), creating a crisp, granular texture along the hardened edge rather than the softer mist () more common in other lines. The surface steel () is forged in tight, irregular wood-grain patterns () often mixed with concentric patterns (), and many examples exhibit a distinctive shadow effect () in which the form of the temper pattern appears faintly mirrored within the surface itself. Within the hardened area, active internal formations such as streaming crystalline lines () and lightning-like bright streaks () frequently occur, providing numerous points of aesthetic appreciation. The tempering in the point () typically turns inward with gentle undulations () and finishes in a small rounded return (), at times showing sweeping lines (). These technical hallmarks appear consistently across the school's production, allowing connoisseurs to identify unsigned works with confidence.
The legacy of the Yoshii school extends beyond its immediate geographical sphere through lineage transmission and stylistic influence. It is recorded that around the Ōei era (1394–1428), several smiths of the Yoshii tradition—including Kiyonori, Naganori, and Yoshinori—relocated to Izumo Province and established the Izumo Dōei school, carrying forward elements of the Yoshii technical approach in a new regional context. The school's ability to maintain its identity even as other groups were subsumed into the mainstream speaks to both the strength of its workshop traditions and the distinctive character of its products. The considerable number of blades that have survived and achieved designation attests to the high regard in which the school's workmanship has been held by successive generations of connoisseurs. These examples—often greatly shortened () yet retaining dignified proportions and sound condition ()—continue to serve as reference standards for understanding the evolution of sword-making during the pivotal transition from the through the period.