Three smiths working at the village of across the second half of the thirteenth century set the terms for every blade that followed: Mitsutada the founder, his son Nagamitsu, and the closely related Sanenaga, the Sansaku triumvirate whose work opens this phase. Their window runs from the mid- period into the early fourteenth century, when leadership passed to Nagamitsu's son Kagemitsu, the third-generation head whose dated , , and carry the phase to its close around the Kenmu years. The repeatedly fix Kagemitsu by genealogy and date, citing pieces inscribed from Gen'o 1 (1319) and Genko 1 (1321) through Shochu and Kenmu (1325 to 1334); these or lightly shortened, date-bearing blades are what give the founding chapter its firm chronological spine and separate it from the workshop-broad output of the later and Oei generations. This is the orthodox mainline before the school fanned out: the generation that built the standard, not the ones that later reinterpreted it.
The constructional signature of the phase is a tightly packed , at times mixed with , carrying fine in dense particles, fine , and a vivid that the examiners single out again and again; one Kagemitsu even pushes the toward a striped, -like with reverse-slanting dark bands. Against the root, with its standing and thicker , this phase reads as more refined and more tightly controlled in the . The temper marks the phase's internal turn. Where Nagamitsu and Mitsutada favored flamboyant , Kagemitsu pulls the hand inward to a -based temper carrying , , and angular elements, often with a reverse () tendency, in a -dominant, bright ; the credit him specifically with perfecting , the dropped-shoulder pattern repeatedly named as his completion. The is the gentle sansaku-, a shallow or turning back in . None of this is the powerful , scattered , and - drama of the later Soden-, nor the open and pointed candlewick of the Oei revival; it is calmer, -bound, and date-anchored.
A collector separates this phase by its named masters and the points the make explicit: and the sansaku- read Kagemitsu, while reverse-slanting and certain forms let the examiners assign proxy hands such as Chikakage and the collaborator Kagemasa, the latter named in a Shochu 2 (1325) joint dedicated to Chichibu Shrine. are a discriminator in their own right, surviving in number for Kagemitsu where they are scarce for Nagamitsu, including the and pieces with devotional and carvings. Provenance present in the sample carries weight: a Kagemitsu transmitted in the Kuroda family with its old scabbard, an recorded in the Shimazu line, and and held in the Imperial collection where Kagemitsu is ranked beside Yoshimitsu, Kunishige, and . These are the works that define the founding core against everything later became.