Shinyaku Toaru Majutsu no Index: Toaru Manatsu no Genten Kaiki

Toaru Manatsu no Genten Kaiki (とある真夏の原点回帰) is a short story written by Kamachi Kazuma that is featured in the Dengeki Super Thanksgiving Leaflet for the Dengeki Bunko Super Thanksgiving Fair 2016 alongside other stories from famous Dengeki Bunko authors.

Summary
Only four pages long, including the cover, the theme of the story is about summer dating.

Full Summary
Touma and Index are walking alongside a lazy river together in swimsuits and begin wondering if what they are doing can be considered a date of sorts. Touma later considers their walk as nothing special as they live under the same roof and cites that if what they are doing is a date then other things they've done like going to limited time sales and should be considered a date as well, annoying Index.

Meanwhile, Index tries to get Touma to notice that she is wearing a swimsuit, and he is trying his best to ignore her body with other matters. Touma later asks why Index was asking if they were on date, to which Index replies that Touma walked past a crepe stand and that the television said that being on a date is where they walk around eating delicious food, to which Touma states that's no different from what they're always doing.

Characters
By order of appearance:
 * Index Librorum Prohibitorum
 * Kamijou Touma

Trivia

 * The illustration for this short story, done by Haimura Kiyotaka, is the same one used for the first BD Box of the Toaru Majutsu no Index anime adaptation.