Shinyaku Toaru Majutsu no Index: A Girl’s Battle (Still Growing) (新約 とある魔術の禁書目録 女の戰 (増量中)?) is a short story written by Kamachi Kazuma that is featured in Dengeki Bunko 25th Anniversary Official Bootleg Book Dengeki Island! (電撃文庫創刊25周年記念！ 公式海賊本 電撃あいらんど!?) for the Dengeki Bunko 25th Anniversary Aki no Dengekisai 2018 (電撃文庫25周年記念 秋の電撃祭 2018?) alongside other stories and illustrations from Dengeki Bunko authors and illustrators.
Only two pages long, the theme of the story is vacation on the South island.
Index and Mikoto meet up before a swimsuit party held by Dengeki. Both of them using pads and other Academy City technology to make them stand out knowing full well that there are characters in the party that have more ridiculous assets than them. Index tells Mikoto to be careful that they do not run into certain characters that are nicknamed "cow" or have titles like "student council president". With this in mind, they plan on approaching a Zashiki Warashi and a "little sister" named Frolaytia so they can stand out in comparison. They laugh mischievously, believing that they have it in the bag, not knowing what those characters truly look like.
By order of appearance:
- South Island
- Despite being on the cover, Kamijou Touma, Shokuhou Misaki, Shirai Kuroko, and Hokaze Junko are not in the story.