Sadayoshi was a principal smith of the Hosho school, one of the five classical Yamato traditions, active in Takaichi District of Yamato Province from the late into the early period. Dated works bearing era inscriptions such as Bunpo, Genko, and Karyaku place his working years firmly within the first decades of the fourteenth century. He signed variously as "Fujiwara Sadayoshi," with the honorary title Kingo, and as Saemon no Jo, frequently incorporating his Takaichi residence into long inscriptions that are of considerable documentary value. Together with Sadamune, he stands as the foremost representative of the Hosho group, which also included the accomplished smiths Sadatsugu, Sadakiyo, Sadaoki, and Sadamitsu, all united by the shared character "" in their given names.
Sadayoshi's work is forged in a thoroughgoing that runs with particular clarity, the straight grain standing out more distinctly than in any other Yamato lineage. Fine adheres thickly, with entering well and a standing often visible along the grain. The is characteristically in which the temper intertwines with the forging pattern, producing frequent , , and , while and enliven the interior. From the upward the tempered width broadens and the grows conspicuously stronger, culminating in a of vigorous that tends toward . The tang is finished with file marks and a blunt tip, both hallmarks of the school. His oeuvre encompasses in , , and the comparatively rare form, occasionally rendered in .
Sadayoshi occupies a position of particular importance among Yamato smiths for the relative abundance of signed and dated works that establish both his place of activity and his working chronology with unusual certainty. His blades have been transmitted in notable collections, including the Hosokawa and Mori families, and carry gold-inlaid attributions by the house. The strongly individual character of his forging and tempering, which the has recognized as the most readily identifiable manner among the five Yamato schools, ensures that his work remains an essential point of reference for the study of the Hosho tradition.