Inoue Shinkai was the second son of the first-generation Izumi no Kami Kunisada of Settsu Province, and was commonly known as Hachirōbei. After his father Kunisada's death, he succeeded to the household and became the second generation. At first, like his father, he signed "Izumi no Kami Kunisada." Around Manji 4 (1661), the Imperial Court granted him permission to cut the chrysanthemum crest () on the tang, and from the eighth month of 12 (1672) onward he changed his name and began signing "Shinkai." It is said that he died suddenly in the eleventh month of Tenna 2 (1682). Together with the toran- of Tsuda no Kami Sukehiro of the province, Shinkai's achievements exerted a major influence on later generations of swordsmiths, and the two are regarded as the supreme representatives of Osaka forging.
Shinkai's manner of workmanship is defined by a tightly forged with thickly adhering and a richly penetrated by , producing steel that is notably clear. In tempering, he favored either a -based with gently shallow , or a mixed with ; in every case the is deep, adheres thickly, and and appear conspicuously, so that both and become bright and clear. His is characteristically tempered rather deeply, often taking on an -like appearance with vigorous at the tip, a treatment that reveals his aspiration toward the mien of classical masterworks. In certain works he modeled the style of Go Yoshihiro -- a manner the describes as Go- -- in which the in both and is especially strong, coarse rises unevenly, and the interweaving of and is "truly striking." Areas of and appear in his bolder compositions, while long-running and lend an unrestrained, rustic vigor. The refined and superior quality of his forging, the depth of , and the brightness and clarity that suffuse both and are, in the 's recurring formulation, "Shinkai's own special domain."
The consistently characterizes Shinkai's oeuvre as the work that "most fully expresses the beauty of workmanship." His finest pieces are praised as demonstrating "the subtle beauty of his " as "Shinkai's unrivaled forte" -- a command of crystalline hardening activity in which "both and are bright and clear" and the achieves an exceptional keenness. The evaluative language across his designated blades returns again and again to terms of luminosity and mastery: forging that is "refined and superior," that is "thick, strong, and well-adhering," and that are "superb" and "truly admirable." Several works are noted as having been forged with "an awareness of the character of the old masterworks he regarded as ideal," suggesting a deliberate engagement with exemplars that elevates his production to the level of scholarly reverence. That many of his blades carry precisely dated inscriptions alongside the imperially sanctioned chrysanthemum crest further enhances their value as documentary material for the study of this smith. Within the broader Osaka tradition, Shinkai stands as the consummate master of quiet, luminous -- the complement to Sukehiro's flamboyant toran- -- and his influence on subsequent generations of swordsmiths is regarded as profound.