Hisakuni (粟田口久国) was the second eldest of the celebrated " Six Brothers" — Kunitomo, Hisakuni, Kuniyasu, Kunikiyo, Arikuni, and Kunitsuna — who constituted the foremost school of swordsmiths in Yamashiro Province during the early period. He styled himself Tōjirō (藤次郎) and was counted among the , the swordsmiths appointed to serve Retired Emperor Go-Toba, a distinction shared with his brothers Kunitomo and Kuniyasu. Beyond this role, Hisakuni is further transmitted as having served as an instructing advisor for the sovereign's own sword forging. Active around the Jōkyū era (1219–1222), he is assessed as standing foremost among the brothers "in both technical mastery and refinement of spirit," and even within the tradition — renowned for producing many outstanding artisans — his work is held to exhibit "the highest level of refinement and dignity." Extant signed works by Hisakuni are extremely few, comprising only a small number of and , with signatures falling into two distinct types: those cut with a thick chisel and those cut with a finer chisel, understood as reflecting changes over time.
Hisakuni's forging is characteristically a finely packed of exceptional density, sometimes described as having a tataki- (consolidated) character, with minute adhering well and fine entering the ground. In certain works, stands out in the . His is predominantly -based, often incorporating extremely shallow and mixing or ; the is deep, with bright well applied. Within the tempered zone the activity is rich: and appear frequently, and enter, and in some works and -like effects are observed. The is consistently described as bright and clear — — and tends toward a suitably tight character. Among the brothers, he is regarded as the smith "whose and most strongly display ; in some works, even somewhat coarse may be intermingled." His is typically straight, turning back in , at times with .
The assessments return repeatedly to a single evaluative axis: the brightness and clarity of both and . This quality — expressed through the term — is identified as the defining characteristic that distinguishes Hisakuni's hand within the broader oeuvre, where " steel is bluish, and the edge is white." His blades are praised for gathering together "the virtues characteristic of workmanship" while possessing "a notably elevated dignity," and unsigned works attributed to him are accepted when they display these features alongside an elegant consistent with an early date. That his works have been transmitted through such lineages as the Matsudaira house, the Kishū Tokugawa, the Date family, and the Imperial Collection attests to the enduring esteem in which his craftsmanship has been held across centuries of Japanese sword connoisseurship.