Japanese eras are named after the reigning emperor, and the Taishō era covers 30 July 1912 to 25 December 1926. It is the period during which Demon Slayer is explicitly set. Most Japanese readers find this immediately, before any character speaks, from the visual coding alone: the women's hakama-and-boots schoolgirl uniforms, the boys' gakuran with brass buttons, the cap-wearing trainmen, the wisteria gardens, the trams clattering past Western-style brick buildings in Ginza. None of these things look 'Edo' (samurai), 'Meiji' (early modernisation upheaval), or 'Shōwa' (war and post-war); they are unmistakably Taishō.

The period is the youngest of Japan's 'pre-war' eras and the shortest of the imperial eras — almost a single generation. Politically it is the high point of 大正デモクラシー (Taishō Democracy): party-cabinet rule, the rise of labour unions, women's suffrage organising, jazz clubs in Asakusa. Culturally it is when Westernised fashion, beef-eating restaurants, station bento, and silver-screen cinema became mass phenomena. Many Demon Slayer setpieces — the Mugen Train, the Yoshiwara red-light district arc, the Asakusa tram encounters — are direct visual citations of Taishō iconography. The era ends with the Shōwa Emperor's accession, after which Japan tips into military government within a decade.

The series uses the era as both backdrop and engine. Demons in Demon Slayer are typically centuries old, which means the Hashira and the demon protagonists are pulled from entirely different time periods even when they share a panel. Rengoku speaks with a register and phrases that already feel old-fashioned to a 1920s reader, let alone a 2020s one — the temporal stack is part of the texture.