In 1941 (Kimetsu no Yaiba)

The infamous gang known as 'the Guerrillas' have plagued the small town of Water's Wake since 1934..

It's 1941 now, and lately, things have only been getting worse. Small crimes such as shoplifting have slowly developed into armed robberies, and many, many acts of gang violence and murders.
Today, the local police department, owned by the Rengoku family, has found a lead. So far, four prime suspects have been identified, all commonly found hanging in slums and densely populated parts of the city.
Makio Uzui.
Her husband, Tengen Uzui.
Obanai Iguro.
And Sanemi Shinazugawa.

Giyuu Tomioka and Mitsuri Kanroji, two underground detectives, have been sent on the case. An undercover mission with only one goal:
Capture the perpetrators.