The second-generation Yasutsugu was the legitimate son and heir of the first-generation Yasutsugu, founder of the Yasutsugu lineage under Tokugawa patronage. His common name was Shimosaka Ichinsho (also recorded as Ichinosho or Ichinoshojo), and in his later years he took Buddhist vows and styled himself Koetsu. He died in Shoho 3 (1646). His workmanship skillfully inherits the manner of the first generation, capably continuing the style established by his father. Like the , he was granted the privilege of bearing the (hollyhock crest) of the Tokugawa house upon his tangs, a mark of direct shogunal sponsorship. He also excelled at producing -mono (emulative copies) of celebrated , including reduced-scale replicas of the famed Ataka Sadamune in -- a form of scholarly reproduction not attempted by the first generation, revealing the Nidai's painstaking effort and ingenuity. Having thoroughly absorbed the style of his father, he also frequently executed ambitious in the Kinai-bori tradition, often attributed to the carver Kinai Tomochika, and many of his blades bear elaborate multi-figure relief carvings in a manner consistent with the first generation's practice.
The technical character of the Nidai Yasutsugu is defined by the distinctive qualities of work. His forging consistently presents an mixed with , tending toward (standing grain), with extremely fine adhering thickly and fine entering well. The steel characteristically shows a dark, blackish cast -- the quality recognized as -- which constitutes one of the most reliable identifying features of the lineage. His most commonly takes the form of or a medium base into which and are interwoven; enter vigorously; adheres well, with patches of somewhat coarse producing unevenness and a broken (basake) appearance. Fine and run through the temper, frequently forming a distinctive striped tendency. The characteristically shows a (subdued) tendency, and is often present along the ridge. His typically returns long and deeply, often with vigorous , expressing a bold spirit in execution. In , his blades range from powerfully built conveying the period flavor of the Keicho era to long of grand and weighty presence, and several examples display the konote-gashiwa manner not infrequently encountered among smiths.
The consistently praises the Nidai Yasutsugu as a smith of superior quality within the early tradition. His works are described as displaying "the characteristic features of work" and "the distinctive features of Nidai Yasutsugu" with particular regularity. Blades of exceptional execution are termed (masterpiece), and individual examples are recognized as showing "an especially outstanding level of workmanship among his works." At its finest, his forging is praised as "excellent for this smith, with a fine and precise texture" and a "bright with well-adhering ." His carvings receive equal commendation: channel work that is "deep," interior carving that is "forceful and vigorous, combining strength with a dignified heaviness," and compositions that differ from the 's arrangements, showing invention and creative intent. The Nidai occupies a secure position as the direct successor who not only faithfully perpetuated the first generation's legacy but also extended it through his own ingenuity in both blade construction and sculptural embellishment, producing works that remain among the most highly regarded of the lineage.