This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / 20th Century Boys
Koizumi and Sadakyo visit the elderly teacher, and he tells Sadakyo that he remembers him and gives him the only picture of Sadakyo's face.
Kenji's song manages to be this without there being any background music (because we all know comics can't make sounds). The scene where we first hear (or see... whatever) him perform it is so beautiful that the volume it's in comes with a CD containing a recorded version (and this was before the movie was made).
Kenji: What are you saying? You've been with us the whole time.
The movie makes the sequence of Kenji and his friends gearing up to battle the Humongous Mecha incredibly moving with the golden age style heroic music playing through the whole thing. These guys know they're not heroes, and they probably won't be able to do anything to stop the mass destruction taking place, and they'll also probably die in the attempt. But damn if they're not going to give everything they have anyway.
Father Nitani's backstory. A Yakuza member on the run in China, he meets a priest who needs to deliver a truck full of medicine to a village in the heavy storm, but can't drive it. Nitani helps him, but only so he can get away from the police. Along the way, he finds out just how much faith the priest has in God. They eventually come to a flooded river, but the bridge over it is too damaged to hold the truck's weight. So the priest gets out and steadies the beam so the truck can drive over. When Nitani gets across, he sees that the priest was washed away, his faith in God not protecting him at all. Nitani manages to get to the village and deliver the medicine, and is hailed as a hero, but he's still depressed about the death of the priest. Despondent, he starts to weep as he holds the bottle of wine he and the priest were going to share when they arrived. Then he sees the priest limping towards him. * sniff*
" I am Godzilla. I have crushed 150,000 people beneath my feet."
Keroyon and his son end up coming across a dehydrated young boy in a seemingly empty town in America. Friend's virus has wiped out literally everyone except for him, and he has been hard at work for days... burying everyone.
Made worse when the boy's worthless father blamed him for bring the Plague to down by selling them out for $150. Keroyon almost had to slap some sense into the boy to make him realize the truth.
The first time we hear Bob Lennon. A few hours before Bloody New Years Eve, Kenji decided to record a song of his on a street corner. He plays with all his might and ends with a quiet "thank you" to an empty street.
All the mafia gangsters that Kanna united tricking her into taking the vaccine so that she'll survive the outbreak, and attempting a seige against Friend for more of the real stuff and her Heroic BSOD after the fact.
"But... there's no news. Nothing at all..."
Speaking of Heroic BSOD, Kanna's first one after she finds out Friend is her father is especially depressing.