Fujishima Tomoshige is the founding smith of the Fujishima school, a lineage of swordsmiths resident at Fujishima in Kaga Province (Kashū). Documentary tradition holds that the first-generation Tomoshige was a disciple of Rai Kunitoshi, though no extant work can be appraised as dating to the Kamakura period, and the NBTHK has observed that "there is no material that can be accepted as confirming this tradition." Alternative sources variously connect him to Kashū Sanekage or Rai Toshimune, but these claims likewise "appear to leave room for further examination." Rather, judging from the workmanship and the manner of tang construction, the NBTHK has concluded that he may be considered to have drawn upon a Yamato-derived lineage. Among dated works, the earliest known inscription is Ōei 2 (1395); however, undated pieces exist whose style "appears to go somewhat earlier," with the oldest works appraised as beginning in the Nanbokuchō period. A single ken bearing only the two-character signature "Tomoshige" is thought to be the earliest surviving work, not descending later than the end of the Kamakura period. The Tomoshige name continued through the Muromachi period and into the Shintō era, flourishing over a long span.

A key point of appreciation in the workmanship of this school is the character of the jigane: it tends toward a slightly standing grain — hada-dachi — and takes on a darkened, blackish tone described as kan'a-iro, presenting a distinctive quality of northern-province workmanship known as hokkoku-hada. Faint shirake-utsuri frequently stands out against this dark ground. The hamon commonly forms a mixed midare in which gunome, hako-ba, and togariba appear together, producing what the NBTHK characterizes as "an impression in which Bizen-like characteristics and Mino-like tendencies coexist." In many works the ashi enter somewhat long and the temper is nie-laden, with vigorous sunagashi and kinsuji running through the hardened edge; small tobiyaki and muneyaki are also encountered. The bōshi frequently shows hakikake and tends toward yakizume. Conversely, among tantō one also encounters works in a fine hoso-suguha with ko-nie — a mode in which the NBTHK has noted points of resemblance to Naoe Shizu and Sekishū Naotsuna, or an Aoe-like manner. The presence of angular and pointed elements within the hardened edge, together with conspicuous sunagashi, are consistently singled out as "points to be appreciated" and essential features of this smith.

Tomoshige is repeatedly designated "a representative smith of the Kaga Fujishima school," and his works are valued both as superior examples of craftsmanship and as reliable source material for understanding the scope of his oeuvre. The NBTHK consistently notes that his finest pieces exhibit ji and ha that are kenzen — sound and well-preserved — and praises blades that "clearly demonstrate the distinctive features of this school and smith." Rare forms such as naginata and large-bodied spears are singled out for exceptional praise; one yari is described as "not only a masterpiece among Fujishima-made spears, but one of the renowned spears representative of its age." Dated Ōei-era works are regarded as "particularly noteworthy" and "exceedingly precious" for establishing his chronology, while pieces appraised as pre-Ōei are valued for pushing the documented range of his career into the late Nanbokuchō period. Through his coexistence of Bizen temperament, Mino inflection, and Yamato structural sensibility — all cast upon the dark, characteristically northern-province ground steel — Tomoshige occupies a singular position among provincial smiths of the transitional Nanbokuchō-to-Muromachi era.