Midoriya goes out of his way to help the ghosts and poltergeists he comes across.
While many ghosts are walking Tearjerkers, the two following Eraserhead are hanging around just to thank him.
Narita was killed by a Serial Killer who he took to ineffectively haunting. Eraserhead not only caught the man, but he also strung him up by the balls the night he tried to kill Narita's sister. For that, Narita will settle for nothing less than thanking the man to his face, no matter how long he has to wait.
Mrs. Kitayama drowned when a villain destroyed a bridge she was driving on. Her son had been in the back seat, and Eraserhead, despite his efforts, had only been able to save one of them.
During the Quirk Assessment Test, several ghosts cheer for Izuku once they realize he can see and hear them.
The day after the USJ incident, Midoriya is certain that his classmates are going to find him weird and creepy for hisactions, only to learn they think he's cool. They also find him creepy but in a cool way.
Midoriya, almost immediately after his vicious match with Todoroki, goes to protect him from a Poltergeist.
After the final exam of the term turns out to have been a real nightmare scenario, Bakugou goes after Midoriya only for Aizawa to immediately intervene. All Might then finds Izuku during his subsequent breakdown and offers not only comfort but sincere apologies for the role he unintentionally played in the whole messy affair. And Aizawa apologizes as well:
Aizawa: "Your classmate's poor behavior is not your responsibility. And fixing it is my job. Trying to shovel some of that headache on you was unprofessional."
The moment where Izuku returns to class and sees that in his absence, Ochako has switched desks with Bakugou so that Izuku doesn't have to sit right behind his bully anymore. (Bakugou's things have been relocated to her old desk, complete with a sign by Sero labeling it tantrum-throwing baby jail.)
When Ochako and Tenya drop by to check on Izuku after the Rescue Arc, it's revealed that Tenya has adopted the little dog he helped Izuku save, naming her Bell.
the fact that Todoroki would rather lose a Hand then Izuku or as he said it It wouldve meant I had to lose a hand for them to take you. But I didnt. is kind of heartwarming in its way, as that level of dedication is only seen in family or lovers.
Izuku briefly panics after unveiling his true Quirk to Todoroki, thinking the other boy is going to call him a liar. But Izuku believed Shouto about his father being a dick, and so he will repay the favor.
Everyone waited for it, and it's finally here: Izuku tells Iida he does see ghosts, and yes, one of them does follow Iida.
Iida: Is—is he... here? Right here?
Midoriya: He never left.
The wonderfulShout-Out to The Sixth Sense. When Izuku answers the question All Might asks when he comes to visit his mentor's grave: yes, Nana is so damn proud of him, the only thing she did right, and it meant everything to her, and Izuku only wants to be worthy of this legacy by being half the hero All Might is. Yagi's answer to this?
Toshinori Yagi: My boy, you're going to be ten times the hero I ever was.
The first thing Izuku does once he tests and confirms he can use One for All to make ghosts visible? Give Iida a chance to talk with his brother again and then gives Nana a chance to finally say everything she's never been able to All Might.
Thanks to Nana and Rei warning him about Overhaul's approach, Izuku can rescue Eri the very first time he meets her.
The author is asexual, and often states on her blog that Izuku and Shouto's queerplatonic relationship is Wish Fulfillment for her. The fact that her readers are so supportive and encouraging of her choice in writing their relationships, while she's usually known for writing them in a romantic relationship, is truly heartwarming.
When facing his death, Sir Nighteye has enough strength to use his Quirk only once with the option to use it on Mirio or Toshinori. It's heavily implied he used it on Mirio and was awestruck by what he saw.
After Sir Nighteye's death, Izuku offers One For All to Mirio, feeling unworthy of it, only for Mirio to reassure him that he deserves his power.
In the same scene, Izuku empowers Sir Nighteye's ghost so he and Mirio can talk.
The final chapter.
Izuku finally sees a therapist - if he really wants to be the next Symbol of Peace, he cannot allow himself to be shut down by stress, as it happened more than once during the story - who is truly professional and doesn't question anything he says.
Izuku meets the child therapist who's taken Eri under his care, and is revealed to be related to someone he knows. He's Rei aka Hitomi's older brother, who was separated from her when they were little. Despite that, and never knowing what happened to her, he's never forgotten Hitomi, and even named his daughter after her. Long before she met Izuku, there had always been someone who cared about her.
Izuku meets Dabi, who since the day he was called by his last name (possibly for the first time in many years) by him in Kamino, has decided to give up villainy and meet his mother. Also holding some of his father Endeavor's secrets gives him leverage to keep his father from further hurting any of his family in the future.
Rather than hold a grudge against Shigaraki, Izuku understands how broken he is and tries to reach out to him. While Shigaraki refuses, the story leaves open the possibility that there may be still salvation for him eventually.
In general, for how darker than the source most of the story has been, by the time of the conclusion the future looks brighter than in canon: Mirio has not lost his quirk, the League of Villains is disbanded, and more than All For One reduced to a vegetative state, it's the death of the Doctor that ensures a lot of the negative developments after the Overhaul arc won't happen.