Saburo Kunimune belonged to the Naomune lineage of Province, the third son of Kunizane, himself a son of Naomune. Known from early times by the sobriquet " Saburo," he was active around the Shogen era (1259-1260) during the mid- period. According to longstanding tradition, he was later summoned by Hojo Tokiyori of the shogunate and relocated to , where — together with Sukezane of the Fukuoka school and Kunitsuna of Kyoto — he became one of the pioneers who laid the foundations of - forging. His works survive in comparatively large numbers, and the question of whether the oeuvre represents a single generation or encompasses successive smiths remains, as the has noted, "a matter that awaits further study," given that -style works bearing Showa-era dates (1312-1317) exist alongside mid- pieces of markedly different character.
The consistently divides his production into two broad modes. The first comprises powerful of wide bearing flamboyant dominated by , with signatures that are large, cut with thick chisels, and rounded in calligraphic style. The second features somewhat slender, gentle forms tempered in calm, -based patterns, with signatures that are smaller, cut with finer chisels, and more angular in character. His characteristically shows mixed with , often tending toward standing grain (), with adhering thickly, frequent , and vivid . In the mode, the is notably tight and bright, with well attached and fine and running through the temper. Among his -ba works, a phenomenon long regarded as diagnostic is the appearance of staining within the hardened edge — a feature "traditionally termed since old times 'the white of Saburo'" ( Saburo no ). Additional hallmarks include (openings at the waist of the ), , and a bosshi that frequently enters with and turns back with or shows .
Across multiple sessions the praises Kunimune's works as displaying and that are — "sound and well-preserved" — with "a dignified and imposing " and "brilliant richly active and varied." His stylistic breadth is repeatedly described as remarkably wide, and individual pieces are singled out for their capacity to illuminate the complex relationship between signature style and blade character, "inviting renewed consideration of the conventional first- and second-generation theory." The Terukuni Shrine National Treasure serves as a touchstone against which other works are measured. In the mode, his finest blades are said to recall "superior works by Unsho" in the brightness and tightness of their — high praise that positions Kunimune at the very heart of mid- craftsmanship and at the origin point of the tradition.