The Senjuin school takes its name from the Senjudo, a hall enshrining Senju Kannon (the Thousand-Armed Avalokitesvara), said to have stood at the western foothills of Mount Wakakusa in Nara. Regarded as the oldest in origin among the Five Schools of Yamato, the group is believed to have been active from the late period, when master smiths Yukinobu and Shigehiro are recorded in old transmitted writings, through the era. The school's deep connections with the religious institutions of Nara -- including Todai-, Tanzan Shrine, and Kyoo Gokoku- (To-) -- are thought to account for the extreme scarcity of signed works, as the smiths served primarily as makers of ritual implements and arms for temple warrior-monks. The oldest surviving signed example, a bearing the three-character inscription "Senjuin," is thought to date to the early period, and pieces prefixed Ko-Senjuin display forms that retain the lingering presence of the earlier chokuto tradition, constituting indispensable material for research into the emergence of the curved blade. Yoshihiro, one of the school's few individually named smiths, is placed in the period with a firmly dated of Bunwa 2 (1354), while Yoshimitsu, recorded from the late period, left works in both and that bear inscriptions of scholarly interest, including the rare character Yamato (倭) and the invocation "Namu ."
The school's collective technical hallmarks are firmly rooted in the Yamato tradition, yet possess a vigor that distinguishes them from the more restrained temper patterns of the , , Hosho, and Shikkake groups. The characteristically shows mixed with and areas of , frequently tending toward ; thick adheres well, with abundant , and in finer examples a faint appears, producing steel of a bright, lustrous quality described as possessing uruoi -- a moist luminosity. The is fundamentally -based with a shallow tendency, into which , , and are mixed; the is characteristically frayed with , and activities such as uchi-noke, , , and appear in profusion. Thick adheres along the , which is bright and clear, while and run vigorously throughout. It has been observed from old times that within the Yamato Five Schools, a of unusually vigorous and changeable character should be appraised as Senjuin. Yet the school's range extends beyond this canonical mode: Yoshihiro's signed works include an exuberant with powerful in a manner that calls works to mind, while Yoshimitsu's display producing an island-like effect along the , demonstrating that the school's individual masters could expand upon the collective idiom with considerable individuality.
The Senjuin school occupies a position of singular importance in the study of early Japanese swordsmithing. Surviving blades encompass , , , , and , the last of these being exceptionally rare as signed examples from this period. Many works retain their , preserving classical forms of pronounced with that overflow with an archaic elegance. The school's served not as weapons of the warrior class but as goshintai and ritual implements, and surviving examples in this form are notably numerous among Yamato works. In both and , the finest Senjuin works display a powerful forging woven through with thick and supported by frequent , combined with a luminous rich in activity -- producing blades that are at once archaic in character and technically outstanding, suffused with the antique fragrance of Nara's sacred precincts.