One interesting scenario could be the characters reacting to modern technology. For example, Sebastian might be both intrigued and a bit disdainful of a smartphone, finding it a curious yet overly complex device compared to the more straightforward tools of his own era. Ciel, on the other hand, could see it as a useful tool for gathering information quickly.
Grell is quite popular as well. His over - the - top personality and his unorthodox views make for some really entertaining reaction scenarios. He can go from being overly dramatic to having some surprisingly deep insights in fanfiction.