Greetings! It does seem almost fanatical today that schoolboys send their severed fingers in protest of a judicial trial for such a high-level assassination. In 1930s Japan however, such public support for right-wing violence and even political assassinations was not uncommon. In fact, The pattern of violence against top-ranking government officials would become so common throughout the 1930s that several historians have referred to the era in Japan as “government by assassination”. Even during the February 26th Incident of 1936, in which a literal coup d'etat was attempted, the government refused to give harsh sentences to many of the army officers involved in the incident (though 19 civilians loosely linked to the coup were later executed). I discuss this "descent into the Dark Valley" more in this three-part response on Japan's interwar politics, so feel free to have a read if interested!

But back to the question at hand. The severed fingers that these schoolboys sent were just one example of the lengths to which the Japanese public would go to in order to protest trials of ultranationalist group members (such as the ones who were involved in the May 15th, Incident, many of which were members of the notorious Ketsumeidan, or "Blood Pledge Corps". It's estimate that the Japanese court which was responsible for the trial of these assassins actually received more than 100,000 letters all across the nation, appealing to the judges that these persons had acted in an honourable and righteous manner. The fingers of the schoolboys were a standout example to be sure, but they had no chance of being taken seriously. What they did lead to however, was a reduction in the final sentences of the "criminals":

• Four years in prison for the eleven young army officers involved,
• Navy Officers: Fifteen years each for Koga Kiyoshi and Mikami Taku as the ringleaders. Only ten years for Yamagashi Hiroshi,
• Civilian Members: Life imprisonment for Tachibana Kosaburao. Fifteen years for Okawa Shumei
• Ketsumeidan members: twelve years for Kawasaki Nagamitsu, eight years for Horikawa Hideo, and five years each for Kurosawa Kanekichi and Terunuma Misao.

Many of these sentences would be reduced even after the trial had finished, with some army army and navy officers even being released the following year after greater public outcry. One other notable figure who even spoke highly of the assassins publicly was War Minister Sadao Araki:

"We cannot restrain our tears when we consider the mentality expressed in the actions of these pure and naive young men. They are not actions for fame, or personal gain, nor are they traitorous. They were performed in the sincere belief that they were for the benefit of Imperial Japan. Therefore, in dealing with this incident, it will not do to dispose of it in a routine manner according to short-sighted conceptions."^(1)

Such was the public (and at times official) mood of Japan as it was gripped by ultranationalist acts of violence and right-wing ascendance. Hope this response helped, and feel free to ask any follow-ups.

Sources

Large, Stephen S. "Nationalist Extremism in Early Shōwa Japan: Inoue Nisshō and the 'Blood-Pledge Corps Incident', 1932." Modern Asian Studies 35, no. 3 (2001): 533-64. Accessed January 10, 2021. http://www.jstor.org/stable/313180.

[1] Quoted in Large. ""Nationalist Extremism in Early Shōwa Japan: Inoue Nisshō and the 'Blood-Pledge Corps Incident'"

Hanneman, Mary L. Japan Faces the World, 1925-1952. Harlow: Longman, 2001.

Gordon, Andrew. A Modern History of Japan: from Tokugawa Times to the Present. New York: Oxford University Press, 2014.