Sanetsugu (真次) is a name borne by smiths across multiple lineages within the western Japanese swordmaking tradition. The most prominent is Ko-Aoe Sanetsugu of Bitchū Province, working in the early Kamakura period within a school traditionally said to have begun with Yasutsugu around the Jōan era. Representative Ko-Aoe smiths — Moritsugu, Tametsugu, Tsugie, Tsunetsugu, and others — share the character "tsugu" as a common element, and Sanetsugu continued for several generations from the Jōō era through the Ōei period. A separate Bizen Sanetsugu, possibly affiliated with the Yoshii line, was active around the Teiwa era of the Nanbokuchō period.
The Ko-Aoe style that Sanetsugu represents is characterized by conspicuous mokume in the forging with a somewhat standing grain, producing what is often called a "chirimen-like" texture. Minute ji-nie adheres thickly, with chikei appearing and a faint utsuri arising. The hamon is typically calm in a suguha mode or mixed with ko-midare, ko-gunome, and ko-chōji-like elements, with ashi and yō; ko-nie gathers in clusters and adheres thickly, while kinsuji and sunagashi occur. Compared with contemporary Bizen works, the nioiguchi tends toward shizumi (subdued), giving an overall impression that is somewhat restrained and austere. The bōshi is typically yakizume with hakikake. A distinguishing structural feature, differing from Ko-Bizen, is that signatures are cut on the ha-ura and tang file marks are in ō-sujikai.
Sanetsugu's Tokubetsu-Juyo tachi, bearing the distinctive ha-ura signature and ō-sujikai file marks, preserves an ubu tachi sugata of high dignity with abundant hiraniku and strongly arched curvature around the lower portion — a distinctive trait of the Ko-Aoe group. The NBTHK has affirmed that every point displays the school's notable features, and that the blade remains in kenzen (sound and well-preserved) condition. His works are valued both for their fine workmanship and as precious documentary material for the Aoe tradition.