The ending of FC is absolutely heartrending, as Joshua reveals his past to Estelle about his involvement with Ouroboros, which ends with him sedating Estelle and promising to leave her alone from now on. Estelle's reaction throughout is what amps up the Tear Jerker quotient so high, as seeing someone as Brightand cheery as Estellecompletely break down is horrible, to say the least.
Estelle: STOP IT. Stop talking about it like it's a dream...! You make it sound like nothing that's happened was even real to you!
Just as bad, if not even worse in some regards, is Joshua's breakdown beforehand upon having his memories restored and being told he was unwittingly feeding Ouroboros intel on Cassius ever since his adoption. FC didn't have much variance in dialogue portraits before this, mostly just a few tweaks to facial expressions... and you're suddenly hit with a portrait of Joshua keeling over, withDull Eyes of Unhappiness. The music, which eventually segues into a slow, sad version of Silver Will, doesn't help matters either. And from Joshua's perspective, even after he regained his memories, he still at least felt the time he spent with Estelle and Cassius was genuine... only to be told this was also all part of Ouroboros' plan. The one ray of light in his life was also a lie.
The end of Chapter 3, where you find out that the Cheerful Child you've spent the whole chapter taking care of was Evil All Along and playing you the entire time. The music (which is the same as in the Tear Jerker moment from the first game's ending mentioned above) and writing does a great job of making the player feel just as betrayed as Estelle.
Loewe's death scene, as he finally realizes why Karin was able to smile when facing her own death, followed by Joshua breaking down after Loewe passes away.
The orchards in Ravennue Village being burned down by Ragnard. Not only is every single NPC utterly devastated by seing their hard work being reduced to ashes in an instant, the village's economy, as one NPC makes clear, is utterly dependent on the trees. Which is to say, is quite unlikely it's going to survive that.
Agate's past deserves a mention as well. His sister died in the Hundred Day War, which he blames himself for, and he even admits that as long as he puts all of his anger directed at himself into his sword it appears he's keeping it together.
The conclusion to Chapter 6 as several characters are finally able to say goodbye to Loewe
Chapter 7 is one long tear-jerker with a couple moments of heartwarming thrown in. The fact that this is the chapter where the game stops hinting at Kevin's past and has him tell the party what happened has a lot to do with this.
You can tell how bleak this part of the game is from the fact that, for the first time in the whole trilogy, there are no joke chest messages. Examining any open chest just results in "the chest is empty".
As part of Chapter 7, Kevin must face all of the sinners he has killed, and the game picks some choice ones. The first is Owen, a corrupt priest from the Church who hired the Jaegers to attack Aster House and who begins his rant by raging at Kevin before descending into a Madness Mantra about how agonizing his continued existence is. The second - and arguably most heartbreaking - is a young boy named Elmer who was turned into a flesh-eating monster by a devil-worshipping cult and who, despite Kevin attempting every form of Thaumaturgy he knew, could not be saved. Upon seeing Kevin and Riese in Gehenna, he begs them to allow him to eat them and sate his hunger; when Kevin states that the least he can do is kill him quickly, Elmer reacts with terror, claiming he doesn't want to die, he just wants to not be hungry anymore. The final miniboss faced is Kevin's mother, now a spectral ghost. The game does an excellent job of showing just how taxing these encounters are on Kevin, seeming to push him to the very brink of completely breaking down without actually cracking his facade.
The game's ending has shades of this. With Phantasmagoria starting to come apart, the characters bid their farewells to one another and, in ones and twos, start heading back through the doorway to the real world. One of the last to leave is Renne, who watches everyone else leave in silence. When Joshua and Estelle ask her about it, she explains that she can't understand why everyone would want to leave instead of just staying in the Hermit's garden and why they're all smiling as they go, even though everyone is sad. As the two of them try to comfort her, she breaks down in tears. Eventually, they explain that they've been looking for her in the real world to make her a part of their family; Renne, taken aback, promises to run away so far that she will never be caught. She dashes through the portal after screaming at them that she hates them... and that she loves them too.
The first chapter of Loewe Monogatari with Loewe, Karin and Joshua living happily together. The Tearjerker aspect comes from knowing exactly what's going to happen in the near future.
The ending of the manga also manages to be this in spades. Seeing Loewe die again has just as much of an emotional punch as it did in the game though it also has a heartwarming moment as Loewe and Karin's spirits watch over Estelle and Joshua