When Lelouch is killed, he is given a choice : continue to descend into madness or save a world from its current course, and turn it into a better world? Only time will tell if Lelouch will change much, but the legend of the man of miracles will be rewritten, for the best or for the worse.

What if, instead of 'dying' at the hands of Arima Kishou, Kaneki was transported into the world Code Geass along with Hide? (Trashy summary, I know. I'm not good at these, I just had an idea.) (there's a little bit of Kaneki x Hide if you squint)