This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Codex Alera
Gauis Sextus' breakdown in Academ's Fury. He's exhausted, strained, rambling and has forced himself far beyond what any human should have to endure. Borderline delirious, he shows Tavi a coastal village, with terrified residents running away only to be swallowed by a magically-induced hurricane. Sickened, Tavi asks if Gaius can help them. He starts destroying things, shouting and screaming about how he can't, he's tried, how he's failed, that he has nothing left to sacrifice and it hasn't been enough. It's the only time we see him completely without his composure and the extent of what the vast burden he holds has done to him.
Gaius Sextus' speech to Aria and Isana during Princeps' Fury. Isana has just clued into how Sextus plans on using her to inadvertently drum up support for Tavi, even though she really can't stand all the politicking he does. It is very effective in driving home the immensity of the burden Sextus carries, how the decisions he has made—especially the one in Kalare—deeply affect him, but also how he is willing to shoulder those burdens so long as they mean the Realm stands.
Isana stared at Gaius for a moment. Then she said, "How can you live with yourself?"
The First Lord stared at her for a moment, his eyes cold. Then he spoke in a very quiet, precise, measured voice. "I look out my window each day. I look out my window at people who live and breathe. At people who have not been devoured by civil war. At people who have not been ravaged by disease. At people who have not starved to death, who have not been hacked apart by enemies of humanity, at people who are free to lie and steal and plot and complain and accuse and behave in all manner of repugnant ways because the Realm stands. Because law and order stands. Because something other than simple violence shapes the course of their lives. And I look, wife of my son, mother of my heir, at the very few who have had the luxury of living their lives without being called upon to make hideous decisions I would not wish upon my worst enemies, and who consequently find such matters morally appalling when they consider them—because they have not had to be the ones that dealt with them." He took a short, hard swallow of wine. "Feh. Aquitaine thinks me his enemy. The fool. If I truly hated him, I'd give him the Crown."
"Fidelias! Behind you!"- and everything that comes after.
"I thought I would be proving your innocence."
Crassus: My mother. Is alive. And you didn't tell me.
For context, his mother was a traitor who was working with the Canim, was betrayed by their leader, and had a discipline collar placed on her by Sarl, who Tavi later killed, making it impossible to remove. As a result, she ended up working as a healer for the Legion of freed slaves allied with the Canim, who at least know what she's going through. When Tavi finds out, she begs him not to tell Crassus, and he keeps her secret...until most of the First Aleran's healers are killed in a confrontation with the Vord queen, with Crassus, Max, and Tavi lethally injured, and she is the only healer skilled enough to keep them alive.
The death of Rook. After everything in the third book, when it finally looks like she'll have a happy ending with her daughter, the fifth book comes along, enslaves her, and callously disposes of her with almost no warning.
The Vord Queen's bewilderment and pain that her junior queens consistently try to remove her.
" I know how a Vord Queen dies. I am ready."
Damn, you, Jim Butcher, how do you do that? How do you make us feel sympathetic towards an unnaturalHumanoid Abomination leading an omnicidalHive Mind? Who murders the aforementioned Rook with no qualms whatsoever?How do you write like that?
The subtext of Tavi and Gaius's strategy session at the end of Captain's Fury. Neither says the words "I love you, I'm glad to have you for my Grandfather/Grandson." And yet the message comes through clearly.