The main character from Attack on Titan, Eren, is revealed to have genocided literally 80% of the world's population (the series states it's 80%, but it's actually a lot worse than that considering he accomplishes this by essentially bulldozing/setting the world on fire so the entire planet's ecosystem is fucked too which means even more people are gonna die) because he couldn't tell his crush, his adopted sister, Mikasa, he liked her. This is despite the fact that what is essentially time-travel exists in the series, Eren has access to it, has used it to change other things in the past before, Mikasa was already head over heels for him, and he has done multiple other things that are extremely more dangerous, and painful like gouging out his own eye, cutting off his own leg, and getting his own mother eaten alive in front of him.
He reveals this in what is essentially an autistic meltdown as posted above, and then his friend, Armin, thanks him for "becoming a mass-murderer for their sake." Then his adoptive sister decapitates him, makes out with his severed head, and then he turns into a bird, and then a tree.
Then the very island he was supposed to be protecting gets nuked by the remaining 20% of the world's population thus rendering the entire story pointless, and lastly the author released a PSA comic telling people to lol calm down, and not take things so seriously.