Aizawa states that he will handle Izuku with Quirk counseling sessions. Izuku, however, is extremely wary of trusting him. Considering most of his life surrounded by teachers who ignored or encouraged bullying against him, he has no reason to trust Aizawa, a Pro Hero with more authority than his previous teachers, will be any different, especially considering his stunt about lying over someone getting expelled on the first day. However, he accidentally voices his thoughts out loud, shocking Aizawa and Ochako. Aizawa decides to make up by saying Nezu and the other teachers will handle the session and he will simply support. Izuku agrees. After he leaves, Aizawa speaks with All Might and is deeply shaken that his Sink or Swim Mentor antics reminded Izuku of his past abusers. He and All Might decide to work together and improve their teaching styles, for Izuku and the rest of the students' sake.
Nana and Toshinori had to learn that despite their best efforts, her family still died. Worse it wasn't even because of her being a hero, but because her grandson's Quirk activating and disintegrating the rest of his family. Then there's the fact Nana has to live with knowing her grandson is a psychotic villain who hates heroes with every fiber of his being.
Made worse by the later realization that this situation was in part caused by All For One's manipulations by giving him that disintegration quirk.
In chapter 25, Izuku reveals he used to have romantic feelings for Bakugo. While he doesn't give details, Izuku mentions that Bakugo "didn't take it well."
Tomura Shigaraki/Tenko Shimura's Redemption Rejection at the mall. He was so traumatized by the deaths of his family and then being overlooked by society in his hour of need that even the realization that All for One has been manipulating him his entire life only makes him double down on being a villain. He accuses Izuku of wanting to talk now that he's a dangerous threat while ignoring the fact that Izuku likely hadn't even been born by the time All for One took him in.
Going by Inko's comments to Toshinori, all of Izuku's classmates stopped coming to his birthday parties after he was diagnosed as Quirkless. He went so long having only his mother to celebrate with that he genuinely has forgotten about his own birthday coming up.
Later, Izuku mentions that until this year, his best birthday in nearly a decade was when everyone just ignored that it was his birthday rather than "doing anything mean" that day.
The original owner of Bonding, Hitoshi Marubashi, had a rough life. Growing up bullied by his classmates, learning he had a Meta Ability at a time those were shunned, forming bonds with other people only for those bonds to snap (usually because of something he did). Eventually, he stopped going to school altogether after getting outed as a Meta. His life seemed to be improving after he met another Meta, Stockpile's owner Shizuku Kendai. Unfortunately, shortly after their wedding, society collapsed, and they had to join a resistance group just to survive the government kill squads and All for One. Finally, on one mission, he was forced to watch his wife get impaled by the crimelord himself and had his Quirk torn from him.
There is also a happy tearjerker: thanks to the final Bond level, Shizuku survived her injury and healed before Bonding's theft. Though, the fact still remains that they were two Quirkless people living in a time of absolute chaos, so they likely didn't survive to see old age.
When Izuku gets shot with the temporary Quirk-erasing bullet, there's a shot of Yui realizing what's happening: for someone who's always had so much trouble expressing herself, Izuku had given her the ability to do so - only to lose it when she was getting used to it.
Related to this is Ochako's cry of anguish when Izuku is taken away just when she was nearly reaching out to him.
After Izuku is successfully kidnapped by the League of Villains, Tomura takes the opportunity to utterly crush Nana by telling her about his abusive father, driving the woman (and Izuku) to tears over how hateful her son grew up to be.
After Izuku demonstrates Smoke Manipulation, Eraserhead is painfully reminded of his friend Oboro Shirakumo, which is made worse when Present Mic points out that Hitoshi and Akira could easily fit in as the equivalents of the two of them. Eraserhead and Present Mic swear not to let Izuku suffer what happen to their best friend.
In Chapter 49, Izuku uses Diagnosis and Overhaul in an attempt to restore the Winged Nomu back to his old classmate Tsubasa. While he partially succeeds, Tsubasa begs Izuku to kill him after the torture he endured. Izuku ends up reverting him back to a simple Nomu, but to Izuku, that was the same outcome.
In chapter 54, the Ennead and the previous wielders infiltrate All for One's vestige realm, in an effort to destroy all the Quirks within it. Things become pretty heartbreaking as soon as they get there.
The vestiges have been there for so long, they forgot their own names, mostly referring to themselves by their Quirk names (Air Cannon, Mute, Megaphone, etc.), and only Quirk Understanding knows their real names by the end of the mission, with Eidetic Memory's death.
It's gutwrenching to see that not only All for One stole their Quirks, but their identities, as if they were never human to begin with.
The fact that the best Izuku and the heroes can do is to give the Quirk Vestiges a quick and painless death to prevent Mugen from using them to hurt innocents. Eidetic Memory (real name, Satoshi Kankura) and Lactic Acid Elimination are two of the few eliminated. Others, like Air Cannon, have to stay behind because they are "favorites" and their disappearance will be noticed.
Neito's thoughts before he jumps in to save Izuku from Nine. It's very clear they are rooted in a massive case of Heroic Self-Deprecation:
"But 1-A had become so much more than they were, especially their green-haired wunderkind. Even their strongest member, Todoroki, seemed to accept that he would be little more than an afterthought compared to Izuku. And that made it clear. He knew how it was. Izuku was important. He wasn’t. He was expendable."
The one who gave Nezu his name and catchphrase was a biology student he met in his youth. Said student would later be killed when she tried to help rescue him from the laboratory where Nezu was being experimented on.
While the Tea Spillers exposing the HSPC corruption with style is an awesome moment, the mood of the video is rather somber, and there is a good reason for it: all of them know they might not live to see another day, since the Commission won't hold back once all of their corruption and misdoings are shown to the world. But, as long as the truth is out, they are alright with it. They know it borders on Thanatos Gambit, and every single one of the vigilantes is okay with that.
During his interview following the HPSC leaks, All Might believes he was an Accomplice by Inaction by not making a clear statement defending the rights of people with mutant and villainous Quirks, as well as Quirkless. He also blames himself for not realizing that the HPSC was using the peace he worked to build for their villainous agenda.
Officer Sansa mentions that despite Mirko and Izuku's interference with the Commission heroes will probably just stay a couple of hours in jail. And worse, it's only a matter of time until police officers like Sansa are forced to help suppress the next rally, something that clearly upsets him.
All Spinner had wanted was a place to belong, with people that actually liked him for who he was. He thought he got that in the MLA, and that Curious actually considered him important. He learns too late that all the "comforting pats" she kept giving him were actually meant to turn him into an Action Bomb against his will. He ultimately dies being murdered by the people he thought accepted him but was at best seen as a tool by them.
It ends up being more painful given that, at least in canon, the League of Villains did hold a genuine camaraderie with him (with the exception of perhaps Dabi), thus further reinforcing his loyalty to them even if it ultimately went to hell in the end with All For One's actions. Here, however, Spinner dies unloved and completely alone, with no one giving a damn about him.
Nighteye's death. While in this story he managed to outlive his canon self over a couple of months, he still dies here, this time at the hands of Slidin' Go during the MLA Uprising. What's worse is that the Liberation mole only succeeded in sneaking up and taking Nighteye out because the hero was too distraught over the Bad Future he witnessed after accidentally using his Quirk on Curious, and was more focused on trying to warn anyone about it to notice his surroundings, and with his death, Izuku and everyone else will be completely unprepared for the terrible events on the horizon.
Right before dying, Nighteye mentions that the future could be thwarted once, so it can happen again. His finals thoughts only rub salt on the wound:
Nighteye’s vision left him as he tried and failed to get words out of his throat. He had to let them know. Had to stop what would come after this. Had to -
Ochako is the one to find his body in the following chapter. While training has prepared her for any gory sights in the field, it is something completely different seeing someone she knows in this situation. She barely has any time to mourn her boyfriend's mentor before being forced to engage Curious.
Himiko Toga makes a reappearance, trying to be a hero like Izuku and begging him to take her back. It's clear that the poor girl, while undoubtedly having done horrible things to innocents and villains, is suffering from a heartbreaking case of Desperately Craves Affection. Izuku ends up crying as he explains that he can't give her what she needs and that she'd have been an amazing hero before knocking her out.
Her breakdown upon meeting him is gut-wrenching to witness.
Himiko: So, can you take me back? Please? I can do this for you… I can fight Villains like you do! I can be a Hero, can’t I? Then you and the girls can love me back?
Mei finds Melissa attempting to integrate Overhaul's healing factor into Battery, the American girl breaks down, blaming herself for not being able to save more people during the fight and letting Izuku take all the responsibility. Mei promptly assures her girlfriend and helps her get over her guilt.
All Might can only find solace that he and Nighteye managed to speak one last time after their fallout, even though they never managed to properly reconnect.
While checking on Tomura's progress, Mugen remembers that Decay's original owner seeked out to him to get rid of the Quirk because he didn't want anyone to get hurt from ir. Mugen takes a sick pleasure seeing the man's Vestige inside Tomura's mind, having witnessed his Quirk being used for so much horror.
The news that the Tea Spillers will eventually get amnesty and become legitimate heroes as a reward for their efforts during the Uprising gets a bitter taste when you realize that Takeshita, Gentle's former friend, is listed amongst the known casualties of the conflict. Now they are never going to be able to meet again.
While it was delayed due to the efforts to help people following the Uprising, Nighteye and other heroes' funerals are held up. It's a rather sight, since the only people in his life that will truly miss him are his sidekicks, Mirio, Izuku and All Might. The man dedicated his entire life to work, and so little is left of him.
Speaking of funerals, Gentle's friend, Takeshita, also has his own, with the Tea Spillers attending to it. While they never got the chance to speak again nor the hero had the chance to remember, it becomes a rather heartwarming Tear Jerker when Takeshita reveals that he refused the chance to go after his former friend (even when the Commission threatened to take his license), because he believed Gentle and his friends were doing way more good with their mission than he ever could.
The now Quirkless Twice tells Izuku that, as much as his Quirk screwed up with his psyche, he still misses it.
Mirio has a breakdown when Izuku confirms his suspicions that one of the reasons Sir Nighteye picked him as a sidekick was to build him up as a candidate for One for All.
Chapter 77:
After Izuku's fight against Tomura's double in the previous chapter, he goes to sleep and talks with Ryouji and Isamu about possibility of having to kill Tomura becoming even more certain. Both of them recall of their own first kills. Isamu had been on the run from anti-meta lynch mob after being tossed out of home, and he had to kill three of them before passing out of exhaustion from his Quirk. A fourth lyncher was about to kill him when Ryouji took the guy out first. After parting ways, Ryouji puked his guts out and Isamu cried himself to sleep. It really shows that for all their dislike over Izuku and All Might's "softness" the resistance fighters never wished to be put through the hell they were forced to go. Nana later shows up and apologizes to Izuku over how her decision protect her son ended up backfiring in such a tragic way, and the both of them end up crying themselves to sleep. It's really tragic how the poor woman has to watch both her blood related and her surrogate grandson having to fight each other to death.
Native's death. While the hero wasn't present in the city during the MLA Uprising, he came back just in time after the Tartarus break out. While out in patrol, Native ends up stumbling upon High End Nomu that resembles a Hound, and the hero just knows he won't make out of the fight alive. That doesn't stop him from trying to take on the monster and get a message out warning othee heroes about it. He manages to seriously fight off the monster at the cost of gruesome injuries and for a second it seems he will make out of it... only for the Elephant High End show up and crush this hope. Native can only find solace he managed to see his family one last time and also that his message got out to warn his fellow heroes before meeting a painful demise at the hands of the Nomus. Nezu later confirms that Native's efforts proved to be decisive point and saved countless heroes and civillians in the process.
While Gigantomachia is ultimately defeated with the combined efforts of Yui and Mt. Lady, by the time the fight is over, the entire city of Ouen-Beru has been completely destroyed. So much damage and countless lives lost, all because no one tried to help a broken and lost boy long ago.
