[[folder: The Lost Hero]]
* Jason is looking through Annabeth's collection of pictures. He asks who the blonde haired boy with her and Thalia is:
-->'''Annabeth:''' That's [[PrecociousCrush Luke]]. [[KilledOffForReal He's dead now.]]
* Heck, Leo's ''whole'' childhood. Accidentally burning his mother alive and then being kicked out by his own family.
** Worse still, [[spoiler: it might look like it wasn't an accident, but Gaea influencing his not-yet-fully-controlled powers...]]
* At the end of ''The Lost Hero'', after talking to her father, Piper thinks something like ''45 seconds? Maybe even a full minute. It wasn't much, but it was a start.'' To repeat: Piper thinks ''a full minute'' alone with her father is good. Busy as he was, despite his good intentions, Tristan [=McLean=] is a bad parent. Being an actor does not [[NoExcuse excuse his lack of attention towards his daughter.]]
* Leo's mother. 'Nuff said.
* Thalia talking about [[spoiler: what happened after Jason was taken away.]]
* Chiron and his promise: [[spoiler: Never to tell anybody about the other camp of Demigods, because last time they met each other, the American Civil War happened.]] Just the fact that he knows, and no one else can, makes it all the harder.
* The degree of manipulation with the memories of everyone especially Jason. Good intentions but still.
[[folder:The Son of Neptune]]
* Percy calls home for the first time in months and gets the answering machine. [[ActionFilmQuietDramaScene He's so visibly upset that both Frank and Hazel are concerned until a monster attacking their train interrupts.]]
** The scene where he calls Juno out for taking all those months from his life, and when he sees his father's shrine also counts. Contrary to the Greeks, the Romans were terrified of the sea. Percy is shaken by the knowledge that not only will he be unpopular here, the campers are ''scared of him''. Thankfully, he bounces back well, saying he has a feeling [[FriendlessBackground it isn't]] [[AbusiveParents the first time]] [[JustAKid he's been]] [[ChildOfTwoWorlds an underdog]]. Still, the reminder of Percy's chronic loneliness isn't nice.
* The later part of Hazel's childhood, particularly her death. [[DeliberateValuesDissonance Suffering intense bullying due to her race and dyslexia]], being held at a distance by her mother, and then discovering that said mother made a DealWithTheDevil and was about to let a very powerful SealedEvilInACan out. So she does [[SarcasmMode what any frightened kid would do]], and sacrifices herself to bury them all under enough rock that it took Gaea another 70-odd years to rise again. Her descriptions of the oil filling up her throat....*shudder*
* Similarly, Gaea drowning Hazel and Percy in muskeg straddles the line between this and NightmareFuel. She traps Hazel in a vision of a perfect, sunny day in New Orleans with her mother-[[UncannyValley whose eyes are blank and mouth is gaping, because Gaea is speaking through her]]. She tells Hazel that she can [[LotusEaterMachine make it so she can live out all the years she missed right here, in the last moments before she dies]]. Grow up, marry her childhood sweetheart, die peacefully in her sleep instead of going back to the arduous life of a demigod. [[RefusingParadise She refuses and screams in the face of a goddess]] once she reminds Hazel that Percy is dying below her, and letting him die will mean throwing a major player right into the enemy's hands(not to mention losing a newfound friend who compared her to family just a few chapters earlier).
** While we don't see it, Percy's half of the equation was equally as awful. Afterwards, when he describes it to Hazel, he's either [[BrokenTears on the verge of tears or outright crying]] just remembering. The consequences stretch through the next book, where he has all the major symptoms of PTSD regarding it, to the point of having a hard time even being around large amounts of water, and fears that if he lets it get too bad, his powers might slip out of his control, or outright disappear. He mentions the fact that Jason can fly and Thalia can't, and she has a severe phobia of heights-so [[FridgeHorror he could actually be right.]] It's a gutwrenchingly realistic portrayal of [[MindRape somebody taking something that was always a source of identity and strength for him and twisting it to hurt him]]. And we don't know if Gaea [[BlackBugRoom showed him things while he was down there]], or [[BreakingSpeech spoke to him]], or if she just let him hang there, slowly suffocating and viscerally aware of his own inability to do anything about it.
* Ella. Poor, poor Ella.
* Mars visits the deathbed of Frank's grandmother and has a talk with him, admitting that Frank wishing someone else was his father is normal, because "nobody welcomes war, not if you're sane." Mind you, this is ''Mars'' talking, respected god of the Romans and father of the founder of their city. Imagine ''Ares'', the butt of many a joke in the Greek pantheon and admittedly TheUnfavorite of Zeus and TheFriendNobodyLikes to everyone else.
[[folder:The Mark of Athena]]
* [[spoiler: Echo staying behind to try and save Narcissus.]]
* [[spoiler: [[YouAreWorthHell "We're staying together. You're not getting away from me. Never again."]]]]
--->"''Tell her hello for me.''"
--->"Hello, Hazel Levesque."
* ''Nico’s eyes looked like shattered glass. Percy wondered sadly if something inside him had broken permanently.''
* Annabeth's story about the [[spoiler: spiders in her bedroom when she was a child. Also NightmareFuel.]]
* [[spoiler: Following the declaration of war between the Romans and the Greeks, the gods all go a bit wonky due to the schism. While most of them are hit very hard by this, Athena takes the cake. When Annabeth sees her, she resembles a slightly off homeless woman and (at least temporarily) disowns Annabeth because of her daughter's insistence that peace can be made between the Greeks and Romans.]]
* [[spoiler: Annabeth falling into Tartarus, and Percy following because [[ThePromise he's promised that he's absolutely not going to lose her again.]] ]]
* What the Romans did to Athena was also pretty horrible.
* On the way towards the Mediterranean, the group finds out that the fabled Pillars of Hercules at Gibraltar are indeed real, manifesting as an island with Hercules himself waiting there. Turns out he is quite a JerkassWoobie: He is at first understanding and says he will only give them a very easy task [[ReasonableAuthorityFigure because he knows what these quests are like.]] He's been stuck on that island for a good while: Back after his mortal essence burned away at the pyre, he was asked what he wanted as reward. He said he wanted to guard the gates of Olympus. [[JackassGenie His wish got him stranded on an island and unable to leave]] as everyone he knew, [[ParentalAbandonment including his father]], left him behind as they left the Mediterranean. He's broken by pressure from the massive expectations everyone has of him, and says that Dionysus, another demigod-turned-god (also his half-brother and fellow posterchild for Hera's hatred of Zeus' children), is the only one that understands him. Then he figures out that Hera brought their group together, and all civility goes away, because he doesn't do what she says. Ever. So he sends Jason and Piper to take the other horn of Achelous, one of Deianeira's suitors who lost her to Heracles. They're trapped on the island with only each other for company.
[[folder:The House of Hades]]
* Everything about Nico. Not only had the poor kid just gotten out of the Greek Mythological Hell Pit, but now we find out that [[spoiler:he's gay (or bi) and has/had a crush on [[IncompatibleOrientation Percy]]. Percy who fell into Tartarus to stay with his girlfriend. Not only does he have to deal with the pain of knowing the person he loves most is going through the horrible trauma that he did, but Nico was born in the 1930's!]] Imagine how ashamed he must feel! It also just ''adds'' to his feelings of isolation.
** The whole scene where this happened was just heartwrenching. [[spoiler:Eros/Cupid, God of Love,]] is just goading Nico on, forcing him to reveal [[spoiler:his true feelings about Percy]], while all Jason can do is listen.
--> '''Nico:''' [[spoiler:I had a crush on Percy.]] That's it. That's the big secret. Happy now?
** And this scene:
--> '''Jason''': [[spoiler:You know, no one's going to judge you.]]
--> '''Nico''': [[spoiler:Really? That would be a first. I'm the son of ''Hades'', Jason. I might as well be covered in blood or sewage, the way people treat me. I don't belong anywhere. I'm not even from this ''century''. But even that's not enough to set me apart. I've got to be- to be-]]
** [[spoiler: He's so ashamed he can't even ''say the word''.]]
*** Now think about this: [[spoiler:Hazel, Nico's half-sister, ''also'' grew up in the 1930s, dying in 1942. Even if he were to accept Jason's more modern sensibilities toward homosexuality, he'd have every reason to believe his sister wouldn't]].
*** And the fact that he's had this conversation before, with ''Percy'', who started out saying Nico would be accepted at Camp Half Blood, but eventually admitted that Nico would never really fit in. And that was ''just'' about Nico being the son of Hades — Percy didn't even know Nico's entire circumstances.
* Annabeth [[spoiler: wandering around blind, thinking Percy's abandoned her while he's forced to watch. Pretty much the entire Curse scene was this with NightmareFuel.]]
* The confrontation with Akhlys becomes this if you take it from Annabeth's perspective. [[FanNickname Dark!Percy]] rearing his vicious head was [[NightmareFuelStationAttendant bad enough already]]. Then you remember that Annabeth has seen this all happen before, the anger, the fear, the festering bitterness-with ''Luke''. Her begging Percy not to touch that power again goes from upsetting to gutwrenching. The poor girl was probably seeing every bad thing in the original series happening over again, another boy she loved losing himself, and probably blaming herself for not seeing it coming and preventing it.
* Leo and [[spoiler: Calypso.]] Full-stop.
* Annabeth overhearing Bob and Damasen talking about how long it's been since they've seen the sun. The way Damasen especially sounds is sad and hopeless because he's [[spoiler:been in Tartarus for so long that he's lost hope to ever see the surface.]]
--> '''Damasen''': Yes. It was yellow. When it touched the horizon, it turned the sky beautiful colors.
--> '''Bob''': I miss the sun. The stars, too. I would like to say hello to the stars again.
** As a matter of fact, Damasen's backstory can be considered a Tearjerker too when you realize [[spoiler:he's only in Tartarus because he was trying to avenge his farmer friend]].
** [[spoiler: Bob says hello.]]
** [[spoiler: When Bob's getting ready to sacrifice himself to let Annabeth and Percy get to the Doors of Death, he tells Percy to “Tell the sun and stars hello for me.” Zoe Nightshade from the previous series was turned into a constellation when she died. Zoe was the daughter of Atlas, who was the son of Iapetus/Bob. It might be untintentional, but Bob was esentially telling Percy to say goodbye to his grandaughter for him.]]
* In the final chapter of ''House of Hades'', Percy tries to thank Nico for guiding the others and for indirectly saving his and Annabeth's lives by being nice to Bob and convincing him that Percy was a friend, even though Percy never gave him a second thought. Percy's trying to live up to his resolution in Tartarus to start treating the people around him better-- he specifically singles Nico out among those. But Nico is being distant and dismissive towards him, and Percy's inner monologue goes on a bit, noting how much Nico has changed over the years and lamenting the fact that he's never been able to understand Nico and he doesn't know why. By this point, [[spoiler:the ''reader'' knows it's because Nico had a crush on Percy, and there's evidence that, despite what he says, he's not really over it and has a hard time dealing with Percy being oblivious, being with someone else, and just the fact that he grew up in the '30s/'40s and is ashamed of liking dudes]]. The tragedy comes from the fact that Percy ''wants'' to understand Nico and do right by him, but Nico just can't let that happen.
[[folder:The Blood of Olympus]]
* Hades telling Nico that few of his children are happy (hoping that Nico will be an exception). You know he's right, and you can see how much it hurts him.
** Doubly tear-inducing because of the contrast with the rest of the series; outside of this moment and maybe a couple from the previous series, none of the gods really seem to care whether or not their children are happy. They care that they survive and bring their parent honor, yes, but not whether they're ''happy''.
** It's a CallBack to ''The Last Olympian'', too. When Hades cursed the Oracle of Delphi, he meant it to last until his children were no longer scorned and ostracized. Hazel's first life was miserable, Bianca was happy for the short time she was a Hunter, then died miserably because she felt guilty about leaving Nico. This is something that's been weighing on Hades for a ''long'' time.
* In ''The Blood of Olympus'' [[spoiler: Nico thinks of the Plato story that once men and women were conjoined but split by the gods because they feared their strength and that was why men and women fell in love. He then asks himself what that means for him.]]
** Even worse if you know the original story: [[spoiler: there actually were both homosexual and heterosexual couples. But Nico comes from a time when homosexuality was actually ''illegal'', meaning most likely the homosexual pairs were deliberately left out of the myths. It makes you think once again how harder coming from the past is making it all for Nico.]]
* Similar to the forced coming out in ''House of Hades'', Percy's confession to Jason that [[DeathSeeker he intentionally endangered himself in battle]] rang a little too true to a lot of readers. While it's unlikely that anybody reading this ever used divine power to choke and torture a goddess, the obvious desperation and self-blame is achingly familiar.
--->'''Percy:''' Thing is, as I was choking just now, I kept thinking: this is payback for Akhlys. The Fates are letting me die the way I tried to kill her. And...honestly, a part of me felt like I deserved it.
* The ending of ''The Blood of Olympus'': amidst all the [[spoiler: heartwarming EarnYourHappyEnding for almost everyone, Reyna ''doesn't'' get one, though she at least gets respect from Athena, Bellona and Pegasus.]]
* As heartwarming as the final chapter was, [[spoiler: Leo doesn't have a way to tell anyone that he's alive after all, so his friends will still think he's dead. We also don't know how much time passes in Ogygia, so even if Leo and Calypso find a way back into the mortal world, it could be years and years since the Final Battle (and Leo's 'death') and Leo could potentially and unintentionally outlive his friends in that aspect.]]
** Even worse, Piper's last thoughts before the start of the final chapter leave it open to interpretation whether the final chapter ''even happened at all''. Which means it's possible [[spoiler:Calypso is once again out there waiting for a hero who will never return for her]].
--->[[spoiler:It might even be possible to tell a new story in which Leo was still out there. Somewhere...]]
** Fortunately in The Trails of Apollo The Hidden Oracle it is revealed [[spoiler:,Leo did come back to life and rescue Calypso, but now she's mortal and has none of her magic.]]
* Apollo cowering before Zeus as Zeus pins the blame for all that happened in the series on him and Hera. Jason even points out in his narration that Apollo looked just like a kid then (perhaps to diminish Zeus's anger), and when he tries to stand up for his half-brother, Zeus gets pissed off (read ''[[AbusiveParents Jason is actually wondering if he will just kill him]]'') at Jason as well. [[CrowningMomentofHeartwarming Despite having said he was proud of him]] moments [[MoodWhiplash before this.]]