Set in a city of scientifically advanced superhuman students, but in a world where magic is also real. Touma Kamijou’s right hand, the Imagine Breaker, will negate all magic, psychic, or divine powers, but not his own bad luck. One day he finds a young girl hanging on his balcony railing. She turns out to be a nun from the Church of England, and her mind has been implanted with the Index-Librorum-Prohibitorum - all the magical texts the Church has removed from circulation.

Index is still a fugitive, and many powerful magical organizations and individuals want to take her to use the books in her memory, eliminating her in the process. War between those organizations is also starting to emerge. Index can only rely on her friend Touma, who has always protected her, along with Misaka and other friends from the Academy.

Science, magic, and a nun on the run! Kamijo and Index return just in time to celebrate A Certain Magical Index’s 10th anniversary with a brand-new season. After their deadly struggle against the Catholic Church and the pending war between magic and science, Kamijo must work harder to protect Index. But with tensions high all around, what new adventures await them in this next chapter?