Witches and Miko: Girls who have obtained magical power (mana from foreign objects) but maintain their reason are called Witches. Those who cannot handle the power, whose minds become contaminated and lose their sanity, are called Miko. To civilians unable to fight, a Miko is a walking disaster. However, to combat-ready Witches, the Miko found around schools are literal punching bags.

Witch Weapon: A form where Witches seal magical power too powerful for them to handle into specific weapons or items. It serves as a safety device to prevent the collapse of the real world and to manage power stably.

Historical Background (1453 Holy Grail War): In 1453 AD, Emperor Constantine XI claimed the 'Holy Grail,' an absolute foreign object. He ruled the world with an iron fist for 500 years through the power of immortality, but in 2033, four Paladins sacrificed their lives to seal the Emperor within the Grail. As a reaction, the world's time reset (looped) to 1453; the Emperor vanished, and only the foreign objects remained in the modern era.

World War III and Academy Cities: In 2027, World War III broke out as humanity weaponized the remaining foreign objects. As the Earth became desolate, six major factions leading the research on foreign objects signed a ceasefire and established 'Academy Cities' that divide and rule one-third of the world's land. Ren lives in the 5th Academy City, 'Shin-Toyosu.'