A CERTAIN MAGICAL INDEX: THE MIRACLE OF ENDYMION

In the movie's story, just before the completion of the Academy City space elevator "Endymion", the main characters Kamijou and Index encounter a level 0 girl named Arisa. The Magicians are after Arisa, and they attack Academy City. A female leader named Shattoaura leads a unit from Academy City against the attack. Kamijou and Index learn from Stiyl that Arisa is key to a brewing war between the sides of Magic and Science. (Source: Anime News Network) — Description from AniList community (anilist.co).