As a result of his father's position, he had the chance to hear Prime Minister Hara Takashi's opposition to extending the franchise.

In late 1923, outraged by the massacre of Japanese leftists and Koreans in the aftermath of the Great Kanto earthquake, he made up his mind to carry out the assassination.

Crown Prince and Regent Hirohito was on his way to the opening of the 48th Session of the Imperial Diet when Nanba fired a small pistol at his carriage.

[2] Although Nanba claimed he was rational (a view agreed upon in the court records), he was proclaimed insane to the public.

[3] His father and his married sister exiled themselves to Java, Dutch East Indies in order to escape the disgrace which Nanba, by his act, had brought upon the family.