The school flourished in the lower basin of the Takahashi River in Province, forging swords at the districts of and Manju in a region long renowned as a source of iron. The school is traditionally held to have begun with Yasutsugu around the Joan era (1171-1175), and works produced from the end of the period through approximately the mid- period are distinguished as , with production continuing under the broader designation through the late era. The representative smiths of this early lineage -- Yasutsugu, Moritsugu, Sadatsugu, Tsunetsugu, Kanetsugu, Toshitsugu, Suketsugu, Tametsugu, Shigetsugu, and Tsugutada among them -- share the character "tsugu" as a common element in their names, forming an unusually cohesive dynastic identity. A distinct sub-lineage, the Senoo group, stood apart from this main line: led by Masatsune and Yukizane, the Senoo smiths forged to the east toward and rarely incorporated the "tsugu" character. Sadatsugu was counted among the serving Retired Emperor Go-Toba, and the Shinkan Hiden-sho assigns the name the highest valuation among works: " workmanship, the finest, fifteen ."
The technical vocabulary is remarkably consistent across its many smiths. The is built on intermixed with , the grain standing conspicuously to produce -- the tightly compressed, crepe-like surface texture that is the school's most recognizable trait. Patches of and mottle the ground steel, while fine adheres thickly with interwoven; a dark-toned may appear amid the standing grain. manifests in several forms across the school's corpus: , , and in certain works by Tsunetsugu, tiered bands suggestive of . The is predominantly -based, mixed with , , and ; adheres well, and fine and run through the hardened edge, while the characteristically tends toward -- a subdued, sinking quality -- or in certain smiths appears bright and clear. The typically turns in , sometimes with . Tang conventions provide critical diagnostic markers distinguishing from contemporary : bold file marks, deeply cut , and signatures placed on the side in characteristically thick chisel work. The consistently observes that compared with works of the era, productions "convey a somewhat quieter and more subdued taste" -- the restrained, astringent character that defines the school's aesthetic.
Yet within this disciplined restraint, individual members demonstrated striking range. Yasutsugu's most celebrated -- transmitted as an heirloom of the Shimazu family and counted among the legendary Tenka Goken -- displays a flamboyant -ba of extraordinary vitality that rivals anything produced in the tradition, while Sadatsugu's finest works invite comparison with National Treasure-class examples. The later Osumi no Gon no Sadatsugu developed a bold personal manner, broadening the , concentrating to produce -like scenery, and tempering the with deep -- features that overflow with vigor. Kanetsugu is praised for almost no unevenness of workmanship across his corpus, while Moritoshi's forging is singled out as tighter and better refined than is typical even within this exacting school. The Senoo branch, represented by Masatsune and Yukizane, carried a flavor somewhat resembling work while maintaining the characteristic and file marks that identify the hand as unmistakably . Across its full productive span, the school stands as one of the foundational pillars of the Japanese sword tradition: a lineage whose refined aesthetic, distinguished crepe-textured forging, and quietly astringent taste secured swords their ancient reputation and continue to command the deepest respect in the study of classical swordsmithing.