Consider: Phantom of the opera au with Jean as Christine, Eren as the phantom, and Reiner as Raoul.
Hi! Sorry for my late reply!
Ohh, Eren obsessed with Jean to the point where he threatens to kill everyone if Jean leaves him? I can see that, both in the Phantom AU and in a canon-divergence AOT AU. His face would, of course, resemble his Titan form, and his eyes would glow behind the mask when he realizes that his love has fallen for someone else. His hatred for Reiner would equal his desire for Jean… You know, I really wouldn’t mind having Reiner in that bad guy role, either—if it weren’t for the unhappy ending, of course.
And they could sing! We were robbed of a musical episode in the series! We could have had it all…