Your main was just sucked into another game or into an animated show.

Who is the champion? What was the game/show? How long would it take them to adapt to their new environment? How would they react?

Hmmm i'm torn between seeing her in RWBY or in Valkyria Chronicles. I'll just do both then :D

RWBY: A world full of Monsters and scumbags that want to conquer/destroy the world. Sounds a lot like Runeterra to be honest minus the schools that train people to defend against said threats I don't think it would take her to long to get settled into that world to be honest even with all of the superior tech they have.

Valkyria Chronicles: Nations at war, Nations fighting with each other internally and racism ALSO sounds a lot like Runterra. It would be extremely interesting to see if Riven would side with Gallia or with the Empire i'm going to go with Gallia because though the Empire is similar to Noxus(Somewhat) the Empire relies to heavily on advanced technology to win wars while Gallia relies more on the skill and experience of their solders something Riven respects. It may take a while for Riven to adjust to her new home in Gallia however.

RWBY: I'm not sure weather Riven would be surprised, impressed, or even both to find out that people who are just barely over 18 are being trained to fight monsters, granted Riven probably isn't that much older then them (Except for Ruby) so she might not be THAT surprised it would however be a MAJOR culture shock to her though.

Valkyria Chronicles: The technology of this world would probably not shock Riven as much as the tech from RWBY would that's for sure I would also doubt that Riven would even try to use a gun, maybe she would carry a side arm but that's still iffy. It would defiantly feel different for Riven as she tries to learn how to live in Gallia, if she even decides to stay in Gallia. I have a feeling she might though such a tiny nation able to hold their own against a military giant? If that doesn't earn Riven's respect i'm not sure what will.

your turn.