Heki Mitsuhira, also known as Hioki Kohei, was originally born in Gamo District of Omi Province and belonged to the Ishido lineage of swordsmiths. According to the prevailing view, he moved from Omi to together with Tsushima no Kami Tsunemitsu, no Kami Munehiro, and Ishido Korekazu, forming the group known as Ishido. However, extant inscriptions — including a blade signed "Heianjo-junin Heki Dewa no Kami Minamoto Mitsuhira" with a reverse reading "Shoo 2, eighth month, an auspicious day; made at Akasaka in , Bushu" — indicate that these smiths did not relocate directly from Omi to but rather first moved from Omi to Kyoto, and only thereafter proceeded to . Mitsuhira has traditionally been considered the younger brother of Tsunemitsu, yet documentary evidence contradicts this: a inscribed with Mitsuhira's age of twenty-nine in Shoho 5 (1648) and a recording Tsunemitsu at seventy-three in Genroku 11 (1698) demonstrate that Mitsuhira was in fact six or seven years the elder. Furthermore, Mitsuhira bore the Minamoto surname while Tsunemitsu used Tachibana; consequently, although their workmanship shares common ground, the theory that they were brothers has come to be questioned. He was born in Genna 5 or 6 (1619–1620), styled himself Heki Shichirobe no Jo, received the official title Dewa no Kami, took the tonsure name Yasunobu, and was awarded the Buddhist rank of Hokyo.
Together with Tsunemitsu, Mitsuhira stands as one of the most technically outstanding swordsmiths representing the Ishido school. His works consistently display a tightly forged or mixed with and , with extremely fine and prominent — a hallmark activity that consciously evokes the classical tradition. His is characteristically a brilliant into which many elements are intermingled: round-headed , , angular forms, , , and , with vigorous and producing a lively, flamboyant tempering of marked height variation. The temper is predominantly , with a that tends toward — tight and bright — and in finer examples, and small appear at the , lending an antique flavor. His is typically gentle, returning in , often with , and the forging may show traces of tendency in the . These last features — the plain and the tendency — are the principal points by which his work, and that of the Ishido school generally, may be distinguished from the masterpieces they so deliberately sought to emulate. His frequently exhibits wide , thick , a suggestion of , and relatively shallow concluding in , producing an imposing, dignified overall bearing characteristic of the transitional period between Keicho and .
In any event, Mitsuhira — together with Tsunemitsu — was among the most accomplished smiths of the period, and there are works in which he forged splendid that call to mind the old masters. Not only the Ishido line but also the Kishu Ishido, Osaka Ishido, and Fukuoka Ishido branches all took the work of the period as their aim, yet Mitsuhira's achievement within this tradition is particularly distinguished. His finest blades demonstrate that, while the pattern tends toward a large-scale design and the internal activities within the tempered area are comparatively scarce when measured against true works, the overall effect is nevertheless brilliantly flamboyant, with no breakdown in the and , revealing a high level of technique. Few of Mitsuhira's works bear date inscriptions; those that survive — including examples from the Shoho and Shoo eras — are exceedingly valuable as documentary material for the study of this smith. Moreover, among his swords many have suffered , making those that survive with intact of particular importance.