Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Tear Jerker: Percy Jackson and the Olympians
Tyson appearing to die in The Sea of Monsters
Annabeth falling and Bianca di Angelo dying, especially when we find out she died to get a toy to give to her little brother, who she had left behind when she joined the Hunters of Artemis
Zoe Nightshade's Heroic Sacrifice, which is made twice as tragic by the fact that it was unnecessary. She died throwing herself in front of Atlas to save Artemis, who she thought was injured too badly to keep fighting. It turns out that Artemis was faking her injury to trick Atlas.
Also, Artemis is an immortal goddess; Atlas couldn't have killed her anyway, but in that moment, to Zoe, it just didn't matter. Her goddess, her best friend, was in danger.
"Let the world honor you, my Huntress. Live forever in the stars."
"Where's my sister?"
Daedalus dying to save everyone else, even if he was a jerk in Battle of the Labyrinth.
Beckendorf dying (you know it's going to happen when he pulls out the photo, but that only makes it worse) and then his girlfriend, who had been completely devastated by his death, dying while posing as her best friend, especially when she reveals that she was the spy the whole time, and thenAnnabeth, who had finally given up on Luke, gave him a knife and had him stab himself to save the world. Luke gets a few more moments of life, then dies, and the villain throughout the whole thing is a hero in the end and his insane mother is waiting for him to come home and... dear God... in The Last Olympian. And that's just the tip of the iceberg, really. And the flashbacks.
—> "We need a shroud... a shroud for a child of Hermes."
And Ethan Nakamura's death. He was a Jerkass, it's sad when he fell off Olympus.
Kronos and the Titans were jerks, but the gods were just as bad. A Tearjerker in sheer fury happens when Athena said something like, "Percy is right. We should not have left our children unclaimed. It proved a strategic mistake and almost brought about our downfall. " Really? Really Athena? Do you actually find it okay to have a random kid and not take the time to get to know and love them? Do you think about how this would affect the kid, or is all you think about how the little demigod child can be used to your advantage?? Argh!!! *Sob*
I think this might be a YMMV because 1) Athena is the goddess of battle strategy, 2) Athena is literally a child born from logic, she is the embodiment of logic, so she wouldn't be all emotional about this, and 3) the gods in general are immortal, and probably have seen thousands of their children born and dead. This is either a coping mechanism or just purely not caring, because honestly, if a person cared for every single one of their children, knowing they'd outlive them, they'd go mad.
Bianca's death, which involved just getting a certain collectible which was missing in her brother's collection, Silena's death and reveal as The Mole, Luke's sacrifice in The Last Olympian, and May Castellan's fate. Percy wonders at the end of the book about her, saying that she will be baking cookies for her son who would never come home. These are just a few examples.
In the film, when Percy and Annabeth arrive at Olympus. Annabeth sees Athena and meekly says "hi, mom" - looking like she's trying not to cry.