The Edo third-generation Yasutsugu was born as the legitimate son of the second-generation Yasutsugu and is said to have borne the name Umansuke. When his father died, he was only seventeen years old, and a succession dispute arose in which a faction sought to install Shiro'emon -- the third son of the first-generation Yasutsugu -- as the new head. Ultimately, the second generation's natural son was confirmed as the third generation, while his uncle Shiro'emon succeeded to the Echizen branch. In this way the Shimosaka family divided into the Edo and Echizen lines, and thereafter each settled and served in its respective domain.

In contrast to the first and second generations, whose work is full of spirit and tends toward a somewhat rough, forceful manner, the Edo third generation's style is more restrained and cohesively composed. His temper typically takes one of two forms: either suguha as the principal theme with a shallow notare flavor, or ko-notare mixed with round-headed gunome. In either case, small ashi enter, the nioi is deep, and nie adheres well, with fine sunagashi and hotsure along the habuchi. A distinctive trait is his use of suguha yakidashi at the base, a feature not seen in the first and second generations. His kitae is ko-itame-hada tightly forged, with areas of mokume mixed in; ji-nie forms thickly in fine granularity with delicate chikei, and the jigane overall shows a blackish, iron-like tone. The boshi is characteristically straight, entering ko-maru with a deep turnback -- a habitual trait inherited from his grandfather and father. Compared with the earlier generations, his forging is tighter and cleaner, the nie adheres evenly without patchiness, and the nioiguchi is bright.

Extant works by the Edo third generation are comparatively few, and blades bearing carvings become rarer still. Among his works there are examples with Kanbun-era dates, though the year of his death is unknown. In his signatures, a habitual trait is observed: as the inscription proceeds toward the nakago-jiri, the size of the characters gradually becomes smaller. His superior pieces express an elegant and calm creative range, and works inscribed with the aoi-mon crest and notations of nanban-tetsu usage attest to the continued prestige of the Shimosaka house under Tokugawa patronage.