Heianjo constitute a technique-defined regional tradition rooted in Yamashiro Province, centered on the capital city of Kyoto. The consistently describe the tradition as one that "draws upon the lineage of Onin ," though the relationship is understood as broadly contemporaneous rather than strictly sequential; the earliest Heianjo inlay works are, in terms of period, close to Onin . The tradition flourished from the closing years of the period through the era and into the early period. Connections to other iron- lineages such as have also been contemplated. From within this milieu emerged Koike Yoshiro, who received the court title Izumi no Kami and took the name Naomasa; originally of Kyoto, he later relocated to Province and is said to have pioneered the tradition known as inlay ( ). Groups of signed artisans working under names such as Nagayoshi, Masashige, Yoshihisa, and Yoshiie are well attested, their inscriptions commonly prefixed with "Heianjo ju" or "Yamashiro no ju."
The collective idiom of the tradition divides broadly into two technical approaches: - (flush raised inlay) and - (flat inlay). A defining characteristic shared by both is the extensive use of brass (shinchu / 真鍮). In terms of design, the - manner frequently employs crests and scrolling (唐草) arabesques developed in an ornamental, pattern-like fashion, while the - manner often depicts grasses and flowers -- chrysanthemum, dianthus (nadeshiko), and bellflower (kikyo) motifs among them. As time progressed, the palette expanded beyond brass to include gold, silver, refined copper (), , and , used in combination; pictorial designs were introduced, and some works mix - with - or incorporate (raised carving in scooped-out relief). The iron plates are typically of generous proportion, and the Koike Yoshiro sub-line is further distinguished by thin iron plates with successive crest openwork at the rim edge, dense - across the ground enhanced with fine line engraving (), and a subtle -otoshi ("set-down flesh") treatment at the rim.
Across the the tradition is repeatedly praised for an unmistakably Kyoto sensibility. Examiners characterize its designs as possessing "an elegant taste" that is "thoroughly Kyoto-like" (kyo-), observing that "from the overall pictorial effect, one can clearly discern an elegant Kyoto taste." The pictorial ambition of later masters such as Nagayoshi, whose landscape compositions "successfully unfold the world of pictorial ," demonstrates the breadth of the tradition beyond pure inlay ornament. Taken together, the Heianjo corpus attests to a sustained metropolitan workshop culture in which brass inlay on iron plate was elevated -- through distinctive technique, refined design, and an abiding courtly elegance -- into one of the recognized pillars of the Kyoto canon.