Heianjo Mitsunaga (平安城光長) was a swordsmith of the late period, active during the Genko era (1321--1324) and working under the toponym Heianjo, the classical designation for the capital at Kyoto in Yamashiro Province. According to and other reference works on signatures and smith lineages, Mitsunaga has been variously said to be of derivation, of the Yamato Shikkake line, or alternatively of the line; however, his exact lineage is not clearly established. Despite this ambiguity, the body of his extant work demonstrates a range that calls both Yamato and Yamashiro traditions to mind, suggesting a smith who drew upon the refined sensibilities of the capital's forge lineages.
An extant bearing a date of Genko 2 (1322) survives as a critical reference point for Mitsunaga's hand. This piece exhibits an unusual construction--- on the front and on the reverse---a rare feature of considerable scholarly interest. His forging typically shows well consolidated, with fine adhering and subtle entering the ground; a faint -like effect sometimes appears. The displays variety across his known works, from narrow -based tempers with mixed in and along the , to shallow with small showing deep and dense . Fine and are frequently observed, and the tends to be bright and well defined.
Mitsunaga's surviving body of work is small but distinguished in quality. Official evaluations consistently note the dignified tone and superior workmanship of his blades, with both and praised as being of good quality and notably . Among works by smiths who prefix their signature with "Heianjo," his dated Genko 2 has been judged the finest. The presence of authenticated signatures is itself considered valuable and rare, adding further weight to Mitsunaga's standing as a noteworthy smith of the late period.