Narimune (成宗) is transmitted as the second son of Norimune, the founder of the Fukuoka Ichimonji lineage in Bizen Province. Active in the early Kamakura period, he belongs to the group of smiths — including Sukemune, Hisamune, Muneyoshi, Munetada, Shigehisa, and Sadazane — who are separately referred to as "Ko-Ichimonji." The manner of workmanship seen in these smiths differs from the splendid, ornate style of the mid-Kamakura Ichimonji masters; in sugata and in the workmanship of jigane and hamon, they strongly preserve the flavor of Ko-Bizen work. His blades characteristically present a slender form with shallow sori and ko-kissaki, often with pronounced koshizori that produces an especially handsome overall silhouette.

Narimune's forging is a dense ko-itame mixed with mokume, bearing minute ji-nie and fine chikei, with conspicuous jihan-utsuri or midare-utsuri standing out in the ji. The hamon is based on ko-choji mixed with ko-midare; abundant ko-ashi and yo appear, ko-nie adheres well, and kinsuji and sunagashi are frequently seen. The boshi tends toward sugu with a rounded turn-back. In signed examples the tang preserves a two-character mei. The NBTHK observes that while his work evokes an archaic elegance, the jigane is notably well-knit with clearly standing utsuri, and the hamon — centered on ko-choji and showing variations in the yaki — vividly reveals the appearance of Ko-Ichimonji.

Narimune's works are praised as displaying the distinctive points of interest characteristic of Ko-Ichimonji. Though calm in feeling, they are blades in which one can fully appreciate the qualities of the early Fukuoka Ichimonji tradition. The ji and ha are consistently described as kenzen — sound and well-preserved — and of good quality. Several examples bear distinguished provenance, including blades formerly transmitted within the Tokugawa shogunal house and others held in the Imperial Collection. His oeuvre stands as a typical and authoritative representation of the early Ichimonji school at its most refined.