(左文字), commonly known as O- or ("Great "), was a swordsmith of Province active in the early period. He is traditionally transmitted as the grandson of Sairen and the son of Jitsua, and the character "" (左) in his signature is understood as an abbreviation of "Saemon Saburo." Since the period, sword treatises have recorded him among the outstanding disciples of Masamune of , and though the validity of this remains open to further examination, - influence is unmistakably present in his work. broke decisively from the older, classical manner of Kyushu workmanship -- a style in which both and tended to be subdued and rustic, with tempering built principally around -- and established a refined, sophisticated idiom not previously seen among Kyushu-made blades. From his lineage emerged many highly skilled disciples -- Yasuyoshi, Yukihiro, Yoshisada, Kunihiro, Hiroyasu, Hiroyuki, Sadayoshi, and others -- each inheriting aspects of the master's manner and flourishing greatly during the period.
The defining hallmark of 's work, repeated throughout with remarkable consistency, is that "both and are bright and clear" (). His shows tightly forged mixed with , with extremely fine (地沸) adhering thickly, abundant (地景), and frequently a standing . The is characteristically based on mixed with , , and pointed elements (-ba); the is deep, (沸) attaches thickly, and conspicuous (金筋) and (砂流し) run throughout, often accompanied by and . The is among his most distinctive features: it rises (), the tip becomes pointed, and it turns back long with vigorous -- a hallmark that "conveys great force." Most extant signed works are , typically small in scale, with shallow , thin , construction, and a characteristically withered (). Among surviving signed , only the celebrated Kosetsu , a National Treasure, is widely acknowledged; signed are exceedingly scarce.
Across the corpus of evaluations, is consistently characterized as having "cast off the earlier classical Kyushu sphere" to establish a style in which both and achieve a lucid brightness and clarity, with as the dominant mode and and standing out prominently. His finest works are praised as displaying "the highest level of technique of the group" and as pieces in which the school's "distinctive vigor overflows." Works of exceptional quality are termed and described as leaving "none of 's highlights unshown." Many of his blades were transmitted within distinguished collections -- the Owari Tokugawa, the Sendai Date, the Tachibana of Yanagawa -- with several recorded in the Kyoho -cho, attesting to longstanding esteem. Sound preservation () and generous remaining blade flesh () are singled out as especially desirable qualities. stands as the transformative figure who brought the - aesthetic to Kyushu, and his achievement represents one of the most consequential departures in the history of Japanese swordsmithing.