Sanenaga is the quiet member of the mainline, recorded in the Kokon Zukushi as a son of Mitsutada and the younger brother of Nagamitsu, and active in the late period. Where his father and brother are read by their flamboyant , Sanenaga is the smith in whom the school's calm straight temper finds its surest hand, and it is in that his work is most confidently identified. The published sources return to the same description again and again: within the group of his time he excelled at a gentle -toned temper, and a hallmark of his work is the well-tightened .
The signature that survives is itself part of the study of him. Blades carry both a two-character signature and a longer one, and among the long signatures are dated works inscribed Shoan, Kagen, Tokuji and Engyo. The Kokon Zukushi places the first Sanenaga in the Bun'ei and Koan years and treats the dated long signatures of Shoan and after as a second generation, though the question of one against two generations is still left open in the published record. The undated two-character pieces are read as the earlier hand, the dated long signatures as the later, and this division gives the connoisseur a rare double anchor of style and date.
The is the refined of the direct line, tightly forged and often mixed with and , with lying microscopically fine and delicate entering the steel. Over it a stands up vividly, and on some blades a more linear, suji-like runs toward the edge before breaking into the form higher up. This is the bright, well-knit the appraisers expect of the mainline, and it is the floor on which Sanenaga's tempering is read.
The is built on a mixed with , and a little , into which and enter; the tends to tighten and carries slight , with fine at times, and it comes up bright and clear. The is the calm point that completes the picture: it goes in with a shallow and turns back small in , the composed turnback that suits the tightened straight temper below it. It is this quiet, controlled finish, , and all of a piece, that the published sources call his typical manner.
A second and rarer manner exists. On a small number of blades the temper opens into a comparatively flamboyant of and , somewhat , close enough that it can be mistaken for his brother Nagamitsu. The tell that keeps the two apart is the , which on Sanenaga stays tighter and cooler in every case; the appraisers note that whichever manner appears, the remains characteristically tight. A few also survive under his name, an uncommon survival shared in the school chiefly with Mitsutada and Nagamitsu.
For the collector, Sanenaga is Sai-jo in Fujishiro's grading, and the record of him is largely a record of the great houses. A signed was transmitted in the Satsuma Shimazu family, carrying a Kotsune noted in the family's 1928 sale catalog; another came down through the Maeda family with a appraisal, and a signed with its passed through the Odawara Okubo house. Ten of his blades stand in the Tokuju tier and forty-two more in , and his work is held in the Imperial collection and through the Date, Shimazu, Maeda and Hosokawa houses. Within his own family he is the counterweight to his brother: where Nagamitsu is plump and flamboyant, Sanenaga is the disciplined hand that shows how refined a plain can be made, and a blade in his calm manner is among the harder names to bring to hand.
