Tomonari (友成) stands as one of the two great pillars of the school, paired with Masatsune as the "twin peaks" of Province swordsmithing in the period. Sword reference works place the first generation around the Eien era (987–989), and it is understood that the name did not belong to a single generation alone: works bearing the Tomonari signature span from the late period through the early period, with a later smith known as the "Katei Tomonari" active around 1235–1238. At least three generations are thought to have used the name, a conclusion drawn from the variety of signature styles — " no Tomonari," " no Tomonari ," "Tomonari ," and the two-character "Tomonari" — as well as from observable differences in and workmanship across the corpus. It is the first generation, however, whose technical skill and dignity of workmanship are considered outstanding and to whom the smith's enduring renown properly pertains.
The consistently characterize Tomonari's forging as or , well forged and sometimes showing a slightly standing grain (), with adhering and, in certain works, appearing. The tends toward a slightly blackish tone — a distinguishing trait noted in contrast to Masatsune. His is typically with mixed in, sometimes enlivened by or ; and enter well, adheres thickly, and within the temper and are frequently observed. The most often runs straight or in shallow , turning in or becoming -like. Where Masatsune frequently displays clearly visible , Tomonari's tends to be faint — some examples show a subtle , while others exhibit little conspicuous at all. Tomonari also favored carving , often rendered kaki-nagashi into the tang, a practice comparatively uncommon in Masatsune's work.
In the traditional comparative appraisal of 's two supreme masters, Tomonari is "especially notable for the excellence of ," while Masatsune is praised for the quality of his forging — a formulation repeated across with near-canonical consistency. The regards Tomonari as the smith whose style is "the most classically archaic" and who "at the time, displays the highest dignity." His works are described as possessing an "archaic elegance" and a beauty of form that is "particularly striking," with workmanship "imbued with an unmistakably archaic elegance." Multiple reside in the Imperial Collection, including the celebrated "Maruguchi," and distinguished provenance attaches to many others — the Satake lords of Kubota, the Mito Tokugawa, the Himeji Sakai, and Tokugawa Iesato among recorded custodians. Tomonari's place at the fountainhead of the tradition is uncontested: his work defines the standard against which the archaic dignity of is measured.