Anti-monarchism has been a minor force in Japan in the twentieth century.
In 1908, a letter allegedly written by Japanese revolutionaries denied the Emperor's divinity, and threatened his life. In 1910, Kōtoku Shūsui and 10 others plotted to assassinate the Emperor. In 1923, and 1925, Hirohito survived assassination attempts that involved Japanese.
After World War II, the communists were antagonistic to the Emperor. The Japanese Communist party demanded the abolition of the emperor system. They boycotted the formal opening of the Japanese Diet (parliament) in 1949 because of the presence of Hirohito. The Japanese Communist Party continued to be antagonistic after Hirohito's death.
During the Royal visits to Otsu, Japan in 1951, and Hokkaido in 1954, Communist posters and handbills antagonistic to the Royal Family Members were plastered in the cities. In 1951, three thousand students in Kyoto University protested against Emperor Hirohito.