is the principal swordsmithing lineage of Oshu (Mutsu province), and the name most representative of the northeastern tradition. Old transmitted records relate that numerous swordsmiths were active in the Oshu region from the Nara period through the period; however, among works that actually survive today, it may be said that virtually only those bearing the name remain. The lineage is understood as a branch of the Maikusa smiths of Oshu, and the name was transmitted over a remarkably long span, continuing from the mid- period through the period and extending well into the period. Among -period works bearing the signature, blades with Oei-era dates are encountered from time to time; when surveyed as a group, extant dated examples include Oei 5, 6, 12, 14, 22, and 25. -period dated works --- inscribed with eras such as Sadawa, Eiwa, Eitoku, and Meitoku --- are rarer still and constitute documents of the highest value for establishing the working range of this tradition. In particular, the Eitoku 2 designated as an Important Art Object serves as a benchmark against which the calligraphic style of other signatures is compared.
The forging of is among the most immediately recognizable in the canon. The characteristically displays mixed with and , with the grain standing out conspicuously --- a quality the consistently terms . Thick adheres, and bold enter frequently, including somewhat thick that are regarded as a particular hallmark of the school. The steel color () inclines toward a blackish tone, often with a faint, whitish cast or intertwining through the standing grain. The is most commonly a temper or shallow mixed with ; the frequently shows , and and appear vigorously. In finer examples the is bright and clear with thick , though in other works it tends toward or --- a subdued, moist quality that the considers characteristic rather than deficient. The typically enters in or with , often finishing with . Carvings are frequently encountered --- , sanko--, with --- and are consistently described as possessing a rustic provincial flavor that nonetheless retains an elegant taste.
In both and , 's work bears a pronounced provincial character that distinguishes it from the metropolitan traditions. The repeatedly observes that the distinctive characteristics of this lineage are "well displayed" or "aptly expressed" in the interplay of standing grain, dark-toned steel, bold , and active within the tempered edge. Pieces of superior forging are singled out as exceptionally fine even among the group's own examples, while those retaining their original tang are noted as particularly valuable. Works spanning from the late through the Oei era are recognized as indispensable reference material for understanding the full developmental arc of northeastern swordsmithing, and the school occupies an irreplaceable position as the sole surviving witness to a once-numerous Oshu forging tradition.