There isn’t much to the story in this book. Misaka and Touma get a room at a hotel to hide from the rain, and end up taking a bath together. It also involves Misaka hugging a cat for ultimate moe-ness.

Full list of related series:
Toaru Majutsu no Index dj - Choudenji Hou no Aishi kata (might not be related)
Toaru Majutsu no Index dj - Railgun no Asobi kata
Toaru Majutsu no Index dj - Choudenji Hou no Sasoi kata
Toaru Kagaku no Railgun dj - Choudenjihou no Mamori kata
Toaru Kagaku no Railgun dj - Choudenjihou no Negai kata

Choudenjihou = Railgun.
In the second story the English word is used, but not in the rest.