Within the of , the place the Fukuoka Ishidō group beside the line as one of the two pillars of the province. The school took root at Fukuoka under the patronage of the Kuroda house, whom its smiths served as domain craftsmen. The lineage's character was set by Koretsugu (是次), born in 'ei 5 (1628), commonly called Hansanbyōe and also Ippei. In Meireki 1 (1655), by order of Lord Kuroda Mitsuyuki, he went up to and studied - under Daijō Sakon Korekazu (Koreichi, 是一) of the Ishidō; three years later he returned to his province and entered Kuroda service. One blade records his aim plainly: the note that he worked chōji-ba strongly in the manner of the school, a deliberate revival of the old idiom in the new era. Moritsugu (守次), son of Ishidō Rihei, apprenticed to his cousin Koretsugu after his father's death; because Koretsugu's heir Toshitsugu predeceased him, Moritsugu is said to have succeeded to the main line. He called himself Gonsabē, later Hansabē, and died in Genroku 14 (1701) at sixty-nine.
The hand is recognized first in the : a dense or that flows overall and, in the lower half, runs strongly to , carrying fine and delicate . Across nearly every blade an stands out, sometimes a , sometimes a straight, -like reflection running along the . The temper is the school's signature: a broad-width mixed with , , angular and pointed () forms, often opening from a or straight into a flamboyant, varied . It is -dominant with , frequently with and , , , , and . The name two diagnostic traits inherited from Korekazu: a tendency in the forging, and that inclines in reverse, the slant. A further idiom recurs throughout the corpus: where the climbs so broadly that the crest reaches the , distinctive forms appear that the records call ika no atama (squid heads), with related pouch-shaped fukuro-chōji and jūka forms also cited. Koretsugu and Moritsugu are named in the as the masters who represent the group; the cooperative signature "Moritsugu · Morimasa," naming Moritsugu and his son Morimasa, is recorded on a , and Morimasa appears there as a working hand of the line.
For , the set out the school's separable points. The -tinged with standing distinguishes these blades from true old , since genuine kosaku do not show this fine ; the tightened with and likewise marks them as rather than . The slant, the squid-head crests reaching the , the deep , and a signature cut in a distinctive long, thick-chiseled hand blending , gyōsho, and reisho are read together as the lineage's fingerprint. is also diagnostic within the group: Koretsugu favored the shallow of the - form, while Moritsugu's blades are noted as comparatively deeper in curvature. The corpus carries several documentary anchors. Koretsugu's dated works run from 6 (1666), including a large hōnōtō votive , through 9 and 11, the last bearing a gold-inlaid futatsu-dō cutting-test inscription naming Shibasaki Denzaemon Masatsugu; one commissioned by Buhei-no-jō Okisuke is tied to the Kōzai line that served the Hosokawa. Moritsugu's Tenna 4 (1684) blades bear the Nanban-tetsu supplemental inscription recording imported iron, and he is recorded executing on works of the province's Yoshimasa. In the register the two cousins stand as the representative makers of the Fukuoka Ishidō, the branch that carried the Ko- into the age.