Mitsutada (光忠) resided at in Province around the mid- period and is regarded as the de facto founder who established the school — historically the largest lineage in the history of Japanese swordmaking. He is traditionally said to have been the son of Chikatada, though no works by Chikatada are known, making Mitsutada in effect the progenitor of the main line. His technical ability was outstanding, and "from ancient times his reputation has been high." From within his group emerged many excellent smiths, including his son Nagamitsu as well as Sanenaga and Kagemitsu, ensuring that the tradition he inaugurated would dominate production for generations. The Honcho Kajiko records that a group in the line of Masatsune resided at , flourished in descendants, and that Mitsutada derived from that stream — a genealogy that certain extant works, with their -like qualities, appear to substantiate through the evidence of the blades themselves.
Mitsutada's characteristic forging is a tightly worked (小板目) mixed with (杢目), in which extremely fine (地沸) adheres in "dust-like" () particles, fine (地景) enter, and vivid (乱映り) stands out clearly. The repeatedly observes that his possesses a particular moisture and luster — an uroi quality — such that, "setting aside the matter of , some can at a glance call to mind Yamashiro workmanship." His (刃文) is characteristically a flamboyant (丁子乱れ) in which - (蛙子丁子), - (袋丁子), (互の目), and (尖刃) intermingle to form a "splendid, flamboyant "; (足) and (葉) enter frequently, the (匂い) is deep with well-adhering (小沸), (金筋) and (砂流し) run through, and the (匂口) is consistently described as "bright and clear." A notable duality pervades his oeuvre: most surviving works are greatly shortened and unsigned attributions displaying bold, powerful (姿) and the most extravagant tempering, while signed tend toward comparatively standard proportions with "more restrained workmanship" — a distinction the identifies across nearly every . This stylistic range extends to blades showing -like traits — standing , thick , and quieter — which the regards as evidence that works "formerly treated as Mitsutada are in fact the very earliest works of Mitsutada."
The accords Mitsutada the highest scholarly esteem, characterizing his finest unsigned works as among "the very finest () of Mitsutada's output" and noting that his blades were prized "from olden times as blades worn by renowned commanders and valiant warriors." The remarkable appraisals by Kochu — including one valuation of one hundred , described as "an exceptionally high valuation for a blade" — attest to his extraordinary standing within the tradition. Individual praise his work as possessing "exceedingly high documentary value," particularly those signed examples that bridge the gap between his restrained signed manner and his flamboyant pieces, and those rare forms such as and ko-dachi that expand understanding of his range. In sum, Mitsutada's place is that of the master who inaugurated what the calls "the single largest school in the history of Japanese swordmaking," and whose output — in the words applied to one of his grandest blades — "seems to presage the flourishing prosperity of the later tradition."
