First off, you made that second post minutes after your first. O_o While PC's an active forum, we're not that awesomely active.
Second, we can't really offer you any characters if we don't actually know what the story's about. Having even an inkling will help us figure out whether we should be submitting comic relief, a main character, someone with fancy powers to help your main character out, or just an ordinary background character.
Third, I wouldn't really recommend doing this. Someone else's OCs tend to be harder to work with than canon characters or your own OCs. The reason why is because you really have no material to work with when you go to write about them. You can't just make stuff up because they're not your characters, and you can't really go and watch an episode or read a chapter of the manga online to figure out how they're supposed to act. So, you're really taking a risk when you go to use a cast that contains characters created by someone else. Unless you're really good, you might actually disappoint people who submit something to you.
Fourth, but if you insist, I'd really suggest going to check out the roleplay forum. They have a lot of games with a lot of profiles that should give you an idea of what to ask for when it comes to characters. In turn, that'll help you get enough information that'll help you write each chapter without having to ask creators lots of questions.
Hope that helps a little!