Yasutsugu was born in Shimosaka-go, Sakata District, Omi Province, and styled himself Shimosaka Ichizaemon. He relocated to and entered the service of Yuki Hideyasu. In his early period he signed " Daijo Shimosaka," but between Keicho 10 and 11 (1605--1606) he was summoned to , where he forged swords before both Shogun Tokugawa Ieyasu and Shogun Hidetada. In recognition, he was granted the hollyhock crest () and the character "" (康), whereupon he changed his name to Yasutsugu. Alternating service between and , he cut "-ju" on works made in his home province and "Oite Bushu " on those forged in the capital. He is known for producing many successful after celebrated masterpieces destroyed in the fall of Osaka Castle; above all, he was particularly adept at copies after Sadamune. The second generation, whose common name was Ichinosho (later taking the tonsure as Koetsu, d. Shoho 3/1646), skillfully carried on the manner of the first generation. Following a succession dispute the line divided into and branches; the third generation (), known as Umanosuke, continued service in .
The forging characteristic of the Yasutsugu line is the so-called : an mixed with and at times , with a tendency toward standing grain (). Extremely fine adheres thickly, enters well -- in places forming thick, kawarigane-like -- and overall the steel tends toward a somewhat blackish tone. The is typically based on or , with connected running in accompaniment; and enter well, and adheres, with fine and appearing. In the upper half, rougher may be intermingled, at times forming mura and becoming slightly basake. Vigorous and occasional or are characteristic, and the frequently shows a (subdued) tendency -- though in the finest examples it is described as bright. The typically enters with a shallow or , with a pointed or Jizo-like turn, vigorous , and a long return. A distinguishing trait is the ko no -gashiwa manner, in which workmanship on and differs markedly.
Across the , the Yasutsugu line is consistently praised for works that "clearly display the typical style" and "characteristic features" of workmanship. Recurring evaluative phrases include "outstanding level of workmanship," "full of force," and "of superior quality." The first generation's blades are noted for powerful reflecting the Keicho period -- wide , little taper between base and tip, shallow , and extended or . His kinai-bori carvings are singled out as deeply cut, forceful, and combining power with a sense of weight. The emphasize that in his copies after famous , the workmanship of and displays his own distinctive style rather than mere imitation. His finest works are described as retaining ample and being in an extremely state. As an official artisan in service to the shogunal house, granted the and the right to use Nanban iron, Yasutsugu occupies a position of the first rank among early -period smiths.