The Shimosaka name began not as a single hand but as a trademark shared by a band of smiths at the dawn of the era, and the designated record gathers their work under that one signature rather than parsing it into individuals. The published sources read the early inscriptions, the generic no Shimosaka and the titled Daijo Fujiwara Shimosaka, as the product of a group, of which the first-generation Yasutsugu served as the representative. Born in Shimosaka village of Sakata district in Omi, Yasutsugu moved to under the patronage of Yuki Hideyasu, signing in his early years no Daijo Shimosaka before his Keicho 10 to 11 summons to , where he forged before Ieyasu and Hidetada and received the character and the right to cut the Tokugawa hollyhock crest on his . The titled signature was carried by several hands at once, and the texts list Yasutsugu, Sadakuni and Kanenori among the smiths whose chisel movement and brush intent are too alike to part on present evidence. From this band the Yasutsugu line descended, dividing after the second generation into the and Shimosaka houses, and around it formed the deep relief carving the province made its own.
The school is recognized first in its steel. The forging is mixed with that stands and opens, often flowing into , carrying thick and fine , the taking on the blackish cast the sources name outright as ; the dark, standing recurs from Yasutsugu through his son, through Sadatsugu, Shigetaka and the unnamed Shimosaka hands, and the commentary returns to it as the group's signature. Over it the favors a to or shallow into which linked and mix, and entering, the thick and gathering unevenly into rough patches, and streaming through, the tending to a sinking . The is the steadiest tell, running to a swept in and turning back long, with a -flavored reminiscence of the and -Seki inheritance. Yet the house is not uniform: Sadakuni works an austere over an unusually refined with little of the blackish , Sadatsugu fires the brightest, most -laden of the circle, and the third generation cleans the forging and brightens the toward his contemporaries. Binding the registers is the carving, the deep -bori and Kinai-bori of , Fudo Myoo, and set in relief within the , which Sadakuni may have first supplied to Yasutsugu's blades.
For the collector the school rewards reading by register rather than by a single famous holding. Yasutsugu is its summit, rated Jo-jo , retained smith to the shogunal house, whose Sadamune and Toshiro copies (the Namazuo, the lost Oyako, the Shishi) show his own hand under the model, and whose best carry the possession inscriptions of his patron Honda Hida no Kami Narishige and provenance in the and Kishu Tokugawa houses. The second generation follows so faithfully that his finest blades part from the father chiefly by the form of the character tsugu; the third generation continues the and manners with a straight and a Hojoji affinity. Around them the specialists define the edges of the idiom: Sadakuni and his quiet with a pair of in the Imperial Collection, Sadatsugu with his Narishige-crested cutting-test blades, and Shigetaka, the most skilled of Yasutsugu's pupils, whose chestnut-tailed and Kinai carving (the Honebami and Hossho copies among his masterworks) name him at a glance and whose finest work approaches the master. A signed Shimosaka blade, whether a titled Yasutsugu beneath the , a named piece by one of the band, or a Daijo pre-Yasutsugu register, comes to market only from time to time, valued as the wellspring from which the Yasutsugu line and its carving tradition arose.