British Halloween

British Halloween (ブリテン・ザ・ハロウィン) refers to the events that occurred in the hours between midnight and early morning of October 18 of the current year of the timeline, where second Princess Carissa of the United Kingdom with the aid of the Knights of England had a coup d'etat, seizing control of the country from her mother Queen Regnant Elizard. Despite the considerable gains of her coup in the early hours of October 18, the resistance forces led by the Anglican Church and with the aid of various other people including third Princess Villian, Kamijou Touma, and Acqua of the Back, pushed Carissa back and the knights to London, where the resistance made one final push against her culminating in the Battle of Buckingham Palace, where the people of London rallied under the banner of the Union Jack held by the Queen to stop Carissa.

The events refer not only to the fighting between the Carissa's faction and Anglican Church but also includes the aggressive maneuvers perpetrated by Carissa's control of the armed forces against France, whom she thought was a threat against the country.

Called the "English Civil War" by the Western fandom of Toaru Majutsu no Index. It is the first major conflict in the story, a prologue of the much larger and longer World War III that starts soon afterwards.