Resident Evil is a series filled with well-loved characters, and Resident Evil 6 seems like a coming together of sorts. With that said, there are still a few more personalities that are yet to be announced, and top of that list (with the exception of Wesker) are Jill and Claire. The producer on the series, Yoshiaki Hirabayashi, was more than ready to tease upcoming reveals.
“We’ve heard a lot of love for Jill and Claire recently and people are asking if they’ll be in the next Resident Evil. There are many other great characters in Resident Evil 6, and we still have some very exciting character information to reveal in addition to what’s already been announced. Until then, you can look forward to seeing how Chris, Leon, Sherry, Piers, Helena and Jake “Wesker Jnr.” take care of things as terror goes global.”
So while Yoshiaki doesn't say "Jill and Claire will be in the game," he's definitely teasing the return of older characters and, personally, I'm hoping for lots of Barry.
