Steel, Guns, and the Industrial Party in Another World - Chapter 405: Old Acquaintance

Uchiha Kai has been cautious since he came to this world. He vowed that he must be cautious and go to the end.

But one day he received a mission – to cover the wave wind team to blow up the Kamabashi Bridge, Uchiha Kai knew that he was going to be unlucky…

- Description from novelbuddy

A series of short stories in the world of Toaru Majutsu no Index organized into chapters featuring Kanzaki Kaori as the protagonist, going around the world and space doing missions for the Church of Necessary Evil, however, there is more than meets the eye as each incident is connected.

One chapter was bundled with each limited edition release of the Toaru Kagaku no Railgun anime DVD and BDs, with all of them together being equivalent to a single normal Toaru Majutsu no Index volume