The Uyoku dantai (右翼団体) are Japanese ultranationalist right-wing groups that advocate for a strong emperor-centered state, traditional values, and an assertive foreign policy; they often emerged in the pre- and post-World War II periods and are known for propaganda activities such as black vans broadcasting patriotic or militaristic messages. One of the most infamous individuals associated with this ideological milieu was Otoya Yamaguchi, a 17-year-old nationalist who, in 1960, carried out a highly publicized assassination during a televised political debate, motivated by extreme opposition to leftist politics and perceived threats to Japan’s national identity.

Inejiro Asanuma was a prominent socialist politician and head of the Japan Socialist Party, known for his outspoken criticism of U.S. influence in Japan and support for leftist international causes. The Anpo protests (安保闘争) were massive nationwide demonstrations in 1959–1960 against the U.S.–Japan Security Treaty (Anpo), which many protesters—especially on the left—viewed as compromising Japanese sovereignty and entangling the country in Cold War conflicts. Asanuma was a visible leader aligned with these protest movements, making him a symbolic target for right-wing extremists; this political polarization, intensified by the protests, directly contributed to his assassination by Yamaguchi, who saw eliminating Asanuma as an act of ideological defense.