The Tatenokai (楯の会, 楯の會) or Shield Society was a private militia in Japan dedicated to traditional Japanese values and veneration of the Emperor.

[3] The private militia was officially founded in 1968 for the purpose of preventing indirect aggression by proponents of foreign ideology seeking to destroy Japanese traditional culture, and protecting the dignity of the Emperor as a symbol of Japan's national identity.

The original members were the staff of New Right monthly magazine Controversy Journal (論争ジャーナル, Ronsō jaanaru) and several Waseda University students.

Mishima decided to increase the size of the private army due to his growing alarm over the scale of left-wing protests in Japan and to this end placed recruitment advertisements in right-wing newspapers.

On 3 March 1977, four Japanese nationalists took 12 hostages at the Keidanren Kaikan (headquarters of the Japan Federation of Economic Organizations), spreading leaflets at the scene that denounced big business.