Toaru Majutsu to Kagaku no Ensemble

The game scenario is written by Kamachi, and is split in four stories: "Magic (Surface)", "Magic (Hidden)", "Science (Surface)", and "Science (Hidden)", with each story having a different protagonist.

In the "Magic (Surface)" story, the Gate of the Gods Descended from Heaven, a Magic Cabal, whose existence is wrapped in a veil of mystery. This story is the one that is featured in Toaru Majutsu no Index: Road to Endymion light novel. In the "Magic (Hidden)" story, the Venus Probe Contest, is a contest in which rockets are launched throughout the world to probe Venus. An event related to that project called the "Venus Probe Project Race" is being held on the Academy City SNS Rondo Net. Here, an incident begins when Kamijou Touma applies for the race. Finally, in the "Science (Hidden)" story, the Academy City SNS Rondo Net is a type of SNS that has grown popular among Academy City students, where registered users can not only communicate amongst each other, but can also acquire things like coupons and for buying things. The number of users of the service has grown explosively. Saten Ruiko has an eye for the current fads, so she tries out the service.

[from Toaru Majutsu no Index Wiki]