Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Tearjerker: The School For Good And Evil
Despite everything that had been said and done, despite all that had passed between them, when it looked like an army of enraged Evers was coming to kill Sophie, Agatha, embracing her, says, "I won't let them hurt you."
Made even more tragic when Sophie replies, "I wish I could say the same."
All of the wolves and fairies were failed Evers and Nevers respectively. And a lot of the kids taken from Gavaldon for the School of Evil weren't necessarily evil, but just rowdy kids, and they wound up having to become the villains of the fairytales we were raised on.