Short answers, pulled from the story.
Yukio Mishima was the pen name of Kimitake Hiraoka, a Japanese novelist, playwright, short story writer, actor, martial artist, and model who lived from the 14th of January 1925 to the 25th of November 1970. He is considered one of the most important postwar stylists of the Japanese language and led an attempted coup that ended in his ritual suicide.
Yukio Mishima died by seppuku, a ritual suicide by disembowelment, on the 25th of November 1970 after a failed coup attempt at a military base in central Tokyo. His second, Masakatsu Morita, failed three times to sever his head, so Hiroyasu Koga completed the task.
Yukio Mishima wrote 34 novels, around 50 plays, and 25 books of short stories, along with more than 35 books of essays. His best-known works include the novels Confessions of a Mask and The Temple of the Golden Pavilion, the autobiographical essay Sun and Steel, and the tetralogy The Sea of Fertility.
Yukio Mishima attempted the coup to inspire the Japan Self-Defense Forces to overthrow Article 9 of the 1947 Constitution and restore autonomous national defense and the divinity of the emperor. He believed Japan's postwar embrace of materialism and Western democracy had cost the nation its national identity and culture.
Yukio Mishima did not win the Nobel Prize in Literature, though he was nominated five times in the 1960s. In 1968 the award went to his countryman and early mentor Yasunari Kawabata, after which Mishima judged that the prize was unlikely to go to another Japanese author soon.
The Tatenokai, or Shield Society, was a private militia that Yukio Mishima formed on the 5th of October 1968, composed mainly of right-wing college students. Mishima funded it with royalties from his writing and capped its membership at exactly 100 members, focused on martial training and physical fitness.