The Akasaka school comprises a lineage of iron tsubako (鐔工) who relocated from Kyoto to the Akasaka district of Edo at the beginning of the Edo period, thereafter flourishing until the end of the Tokugawa shogunate. The founding master, Shozaemon Tadamasa (忠正), is traditionally held to have been active from the Kan'ei to Meireki eras (1624--1658); a genealogical statement (yui-shogaki) submitted during the Bunsei era records that shodai Tadamasa died in Meireki 3 (1657) and nidai Tadamasa in Enpo 5 (1677). The so-called "upper three generations" (jo sandai) of Ko-Akasaka -- shodai Tadamasa, nidai Tadamasa, and sandai Tadatora (忠虎) -- produced no confirmed signed works. It is only with the fourth generation, Hikojuro Tadatoshi (彦十郎忠時), around the Genroku era, that signed pieces appear, bearing inscriptions such as "Bushu-ju Akasaka Hikojuro Tadatoshi saku" (武州住赤坂彦十郎忠時作); thereafter, through the ninth generation, the main line continued to bear the name Tadatoshi. A notable branch was established by Tayuemon Tadashige (太右衛門忠重), who entered the school under the fourth-generation Tadatoshi -- his practical teacher being the fifth -- and whose eldest son Tadayoshi (忠好) carried on his line.

As iron ji-sukashi (地透) tsuba makers, the Akasaka school is renowned alongside the Kyoto, Owari, and Higo traditions. In the school's ironwork one encounters a forging method referred to as sanmai-awase (三枚合わせ), a form of composite laminate construction. Their subjects frequently express natural scenery, famous places, and episodes from classical precedent (koji), rendered through inventive designs: established motifs include Hachi-no-ki, Shiguretei, Musashino, wind and bamboo, praying mantis, interlocking rings, and aged pines. In construction, the plate's nikuoki (肉置き) typically rises to a gentle central swell (nakadaka); the connecting bridges of the openwork broaden near the rim, producing a stable visual balance; and the rim is customarily finished as a rounded maru-mimi (丸耳). The seppa-dai narrows toward the top into an almost pointed form, and the kogai-hitsu is typically smaller than the kozuka-hitsu -- a diagnostic feature especially pronounced in works of the first and second generations. In the earlier Ko-Akasaka phase, the workmanship is marked by a calm, restrained tsuchime (槌目) finish and a powerful maru-mimi, with designs unconstrained by strict symmetry, showing instead a free spirit and tenacious strength; one can sense the influence of Kyo-sukashi, Owari-sukashi, and early Ko-Shoami. The openwork carving possesses a distinctive, sharply pointed character, and striped iron bones (tekkotsu) visible on the rim further convey an old style of pronounced dignity.

One of the principal attractions of Akasaka tsuba lies in the novelty of their compositions, and in this regard the school's most celebrated later master, Tadashige, is outstanding. A long-lived artisan whose late-life signature "at the age of eighty-four, made by Tadashige" (行年八十四才・忠重作) is recorded, he has been praised as among the finest of all Akasaka masters from the fourth through ninth generations. His progressive temperament led him to incorporate decorative pattern ideas associated with Ogata Korin, and his designs -- such as the sankai-matsukaze (三階松風) motif, which is his own invention "not found even among Higo tsuba" -- demonstrate a striking originality within the iron sukashi idiom. His work displays a characteristic reduction of volume at the rim edge, superb forging, and a patinated rust tone possessing a distinctive sheen. Together with the dignified unsigned works of Ko-Akasaka and the refined productions of Tadayoshi, the Akasaka school's body of work testifies to a tradition that synthesized the elegance of Kyoto openwork with the strength of Owari into a distinctive Edo aesthetic -- one whose "true specialty," in the words of the NBTHK examiners, "is a stylish and tasteful openwork aesthetic" (iki na sukashi o honryo to shita).