This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / Ender's Game
Ender's Game: "The most noble title any child can bear is third", " I didn't want to kill anyone — why wouldn't they leave me alone?", " He fought with honor. I didn't fight with honor. I fought to win.", "Do they know me well enough to know I don't fear death?"
Ender: In the moment when I truly understand my enemy, understand him well enough to defeat him, then in that very moment I also love him. I think it's impossible to really understand somebody, what they want, what they believe, and not love them the way they love themselves. And then, in that very moment when I love them... I destroy them. I make it impossible for them to ever hurt me again. I grind them and grind them until they don't exist.
From the movie, when Ender is confronting the Hive Queen just inches from her egg. She reaches a claw out to, presumably, kill Ender to avenge her species. But she stops, and withdraws her claw, gently stroking his face instead. The single line that Ender speaks to the Queen clinches it. May also double as a Crowning Moment of Heartwarming.
Ender: "You're dying..."
"Mother. Father. Did I do it right?"
By the end of "Ender's Game," Ender believes his parents had forgotten him. In a short piece by Card, we find this isn't true and that Ender's parents, who are still very much pining for their son, took some measure to keep Ender off Earth to protect him.