Here is a couple that "should've been" from my favorite novel, manga, and anime Trinity Blood. Abel and Esther become very close friends in the story, and Abel would do anything to keep her safe. They are unable to have a relationship due to their occupations, Abel (priest) and Esther (nun). If it were up to me they would somehow and someway be together. So here is our closing "should've been" couple of the week (also my favorite) Abel and Esther!