This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / Guild Wars 2
Each of your Order mentor's death:
Magister Sieran (Durmand Priory): A very happy-go-lucky Sylvari who was in love with the world, and had a tendency to say 'cherry!' when she was happy about something. She treats her death as another adventure, and says she is excited to see what awaits her in the Mists, but you can tell she's terrified.
Lightbringer Tybalt Leftpaw (Order of Whispers): A very easygoing charr engineer, who, despite being a member of the Order for some time, did his first field mission with the Player Character, and rejoiced when he is assigned to permanent field duty. A complicity slowly grows between him and the PC, with this odd charr who has a fondness for apples, who has insecurities linked to his missing right pawn (which blew up a few years ago), and reveals to the PC that his partnership with him is what gives him the courage to stay in the field. He sacrifices himself in order to help you escape from Claw Island. During a later mission defending the Order of Whispers from a Risen assault, it is revealed that the security system was designed by Tybalt, and that the password to override the system is apples.
Warmaster Forgal Kernsson (Vigil): In contrast to the other two, Forgal acts more as a stern father-figure to your character than a good friend. He softens up gradually, showing more and more how proud he is of you, until you learn at Claw Island that he had previously lost his family, meaning that he as a norn had no one to tell and pass on his legend until you came along. He thus decides that keeping back the Risen while you escape will be a worthy death, and entrusts you to tell it while he walks back into battle again a dragon-champion and a huge number of Risen.
This comes back to haunt your player character in the penultimate story mission where you fight ANOTHER GODDAMN EYE OF ZHAITAN. In addition to not wanting to fight another goddamn Eye of Zhaitan for the nth time, he taunts you about your dead mentor and says that he or she is "waiting for you now, beneath the dragon's wings..."
The events that transpire if, during the mission 'A Light in the Darkness', you told the Pale Tree that your greatest fear is "letting an innocent die", in particular 'A Sad Duty'. At the end of the mission chain leading up to the Battle of Fort Trinity, your partner, the Asuran demolitionist Tonn, sacrifices his life to destroy the Orrian Bone Ship, swimming back out to fix the explosive charges and telling you to set them off while he's still in range. After the Battle at Fort Trinity, you accept the duty of telling his beloved wife Ceera, a Pact field medic who Tonn constantly discussed with you fondly, of her husband's death. The news destroys her, almost driving her to suicideto join him and she swears never to forgive you for causing his death. While you manage to save her, when you leave her she's helplessly sobbing her eyes out alone. For those who question whether the Asura are capable of either true heroism or truly caring about anyone other than themselves, this mission will set you heartrendingly straight.
Snaff's death, and the disbandment of Destiny's Edge. Along with the fact that the dragon Glint is also dead. The events closely following after the deaths were quite heartwrenching for this troper.
Eir being told that her whole plan failed and that she killed Snaff.
Eir: You can't die! Zojja: He's already dead. Eir: You can't die. (takes Snaff's body from his golem and cradles it) Zojja: Put him down! You have no right! Your plan failed. You killed him! Eir: I killed him?
Zojja having to cremate her own master's body. And her exchange of words with Caithe after gathering his ashes:
Caithe: Rytlock is leaving. Zojja: Just like Logan. Caithe: We have to stop him, or go with him. Zojja: I don't have to do anything. Caithe: Don't be irrational. Zojja: Who are you to tell me anything? You're not my master, my master is dead. Caithe: This could be the death of the whole world. Zojja: My world is dead.
Rytlock realizing that all their efforts were pointless and that he was a fool for trusting Logan.
Caithe's efforts on trying to keep the group together, which miserably failed. Until now, at the present time of the game, she still attempts to do so. And all those attempts failed as well.
In a different timeline when the Pale Tree presents a vision of Orr to the Player Character, you find that she's grown so tired of rounding them up only to fail again that she decides to join Faolain in the Nightmare Court.
The fact that a number of the allies (Lionguard Apatia from Claw Island, Kekt from the undead ambush in Ural's Delve and so on) you met, usually from earlier missions, started dying in the personal story missions for levels around 70-80 is just really, really sad...
It gets sadder when your other allies have put all their trust in that person or when you find out they've been turned into Risen or when you find out that that person looked up to your Player Character.
The sight of fallen refugees in the first Living Story update. Flame and Frost added a few NPCs around refugee camps in their cities. One of them, the Refugee Primus, mentions how the cubs he was watching over were killed. Also, the general idea of the refugees being completely beaten down by the disaster and forced into rat-infested camps in their capitals.
One particular event in Straits of Devastation requires you to clear out a field hospital of Risen. After the event is completed, we get this exchange:
Commander Blaike: Status report. How many of our sick and injured did we lose? Medic Kellye: All of them... sir. Commander Blaike: I... I see. Repair the damage and prepare to receive more casualties.
What really sells it is the way Blaike's second line is delivered, with the perfect blend of horror and realization, yet still remaining partly stoic in the face of crisis.
November '13 addition, living story "Fractured", has one near the end - when you realize the hub instance you go through every time when you're in the Fractals of the Mists, is nothing else than Dessa's own personal fractal.Just before that, Dessa muses on the fate of her krewmates from Thaumanova, who have to relive the same moment in their lives (in their case, death) every time someone activates their fractal.
Lion's Arch in the aftermath of Scarlet's attack. The place is in ruins, the music is very sad in tone and lots of NPCs are either greiving, confused, have left notes for lost loved ones or are digging graves for the fallen.
There was a noticeboard where survivors left notes to try and reunite with missing loved ones. After reading a few, the last one is written in the handwriting of a young child, and it says "I can't find my mommy or daddy."
Heart of Thorns has many, many moments.
The way the sylvari are being treated. This varies from suspicion and coldness to Pact vigilantes kidnapping sylvari troops to murder them. It's hard not to feel sorry for them.
Pale Reaver Scout: Please, don't hurt me.
The death of Eir Stegalkin, and Braham's reaction.
To add to this, Garm is still missing.
The revelation that Rata Novus is nothing but a dead city.
The scene where Taimi gives up Scruffy. Making it even worse is how Scruffy hesitates, apparently needing reassurance.
Finding Logan and Zojja is both reassuring and heartbreaking. They have clearly suffered.
In the final battle Mordremoth summons versions of the companions you left behind in other to fight you. Their dialogue is one of despair while keeping their personalities. But the worst is when he summons your Order's mentor (Tybalt, Sieran or Forgal). The commander is absolutely pissed at this action. A happier version happens at the end when you purify the phantom and they join you in the fight.
Tybalt Leftpaw: It's good to see you, my friend. Player Character: I've missed you, Tybalt. Grab an apple and let's finish this!
Finding Trahearne, who is too far gone to save. He just sounds so exhausted. His friend, the Commander, is tasked with killing him with Caladbolg. The beginning of 'Fear Not This Night' plays softly as Trahearne asks for the sword.