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Tear Jerker: Shakugan no Shana
Shakugan no Shana has one very early on; not even halfway through the first season, we are treated to the permanent disappearance of Yukari Hirai. And here, "permanent disappearance" is NOT a case of Never Say "Die". Her very existence will slowly vanish from everyone's memories, and when everyone forgets her, it will be as though she never existed at all. We get to watch Yuji try to prevent this. We get to watch her go from The Cutie in one appearance to Emotionless Girl in the very next. To the point where she barely acknowledges the same guy she was hopelessly in love with, and Yuji is happy because this is better than her now-usual reaction. Yuji at one point gets her to take a photo with her aforementioned Love Interest, which she is holding...when she finally disappears. And when Yuji picks up this photo, he doesn't see her in it, despite the fact that she just vanished right next to him.Damn.
It's made even worse because the entire sequence of Yuji trying so hard to help Hirai is set to happy, hopeful music, as though maybe, just maybe, she might have a chance, and every little sign of excitement or happiness from her is so heartbreaking, because it shows that Hirai really is in there somewhere, but she's fading so fast...
The part when Yoshida yells at Ogata for forgetting about Konoe after she got Ret Goned, only for the extremely confused Ogata to sadly say she has no idea who she's talking about.
Khamsin's backstory. He was once the Warrior Prince of an ancient kingdom. When a Crimson Denizen attacked, he made a contract with Behemoth to become a Flame Haze so he would have the power to fight back. He drove the monster off, only to find that no one in the kingdom, not even his own father, remembered him anymore. Khamsin vowed revenge on the monster for forcing this to happen and spent several years hunting it. With each rematch, he and the monster slowly got acquainted. When he finally killed it, he realized the only other being besides Behemoth who remembered him and the closest thing he had to a friend was now dead. When Khamsin dies, he wonders if he and the monster will finally meet again.