Even if the world is full of superheroes and goodwill, there is always a dark shadow that will show the true reality of this world. And the same can be said for these various jokes and details that soured as the series continues.
- The Luminescent Baby whose arrival ushered in the Age of Quirks? All For One stole that Quirk and then killed them for being famous for the arrival of the Age of Quirks.
- When Midoriya's attempt to attack the Sludge Villain proves ineffective by itself, and he only escapes because he shamed All Might into acting, he ends up getting chewed out by the heroes after the incident is resolved. Gentle, as Midoriya's Evil Counterpart, was similar in that he tried to save someone, only to fail and inadvertently make things worse. If Midoriya hadn't been as lucky as he'd been, his life and reputation might have been ruined if he'd been judged to have interfered with a hero's work.
- When Twice was introduced, his goofy antics and odd mannerisms quickly made him an Ensemble Dark Horse, with many fans pointing to Deadpool as an obvious comparison and inspiration. Come Chapter 115, we get to see him without the mask, and we find out that his antics are a side effect of having been mentally broken through suffering an Ambiguous Clone Ending... of his own doing, due to misuse of his Quirk. Behind the mask is a conflicted and self-loathing man suffering from a split-personality who doesn't even know if he's the original.
- Less than a week after the anime gets to where All Might loses his powers and his position as #1 hero, we get Chapter 188, which ends with his successor, Endeavor, suffering a really bad injury. It makes his "You're next" line unfortunate.
- In Chapter 160, Dabi refers to Spinner as "Lizard," to which Spinner takes offense. In Chapter 220, it's revealed that for most of his life, Spinner has been discriminated against due to his appearance and labeled as "Dumb Lizard Man" by people with old-fashioned values. The same information also puts some details about Tsuyu and Shoji's past into a much harsher light, such as Shoji having to hide his face to not scare others, seemingly never removing his mask, and Tsuyu having a hard time making friends because she was ostracized from the other girls' circle of friends.
- The context of Shoji's past is revealed during his fight against Spinner during the Final War arc, as he was harassed and brutally attacked in his old village home, even after saving the life of a human girl. This is why he brushed off Mineta casually calling him an octopus at one point, which the smaller student regrets, and later with Pony Tsunotori of Class 1-B when she compares him to an octopi in an aquarium. Before the arc began, he was seen interacting with the "Ordinary Woman", another Heteromorph who was recently caught in a biased attack before Midoriya rescued her, now having someone to relate to.
- The Shie Hassaikai wear Plague Doctor masks to emulate their germophobic leader, and Yu Hojo of the Garbage Trio wears a standard surgical mask. In the COVID-19 pandemic, mask-wearing became a much more common practice to help contain the spread of the virus.
- Jokes about Shigaraki's hand-themed design, calling him "Handyman", "Handjob" or "Facepalm", get a lot darker when Chapter 222 reveals that those hands are all that are left of the family he accidentally killed with his Quirk.
- Belief both in-universe and out that Mirio was a more worthy holder of One For All was rendered this in Chapter 304, where the previous holders of One For All acknowledge that Midoriya was the perfect choice for being the holder of One For All due to his Quirklessness. Mirio, or any other Quirked individual, would die roughly 20 years after gaining it due to having it along with their original Quirk forcing their body to engage in Rapid Aging.
- Every instance of characters like Bakugo and Aizawa telling Midoriya he doesn't belong in U.A. High and that he should leave becomes this after the Paranormal Liberation War, since Midoriya is forced to drop out of U.A. to keep his loved ones safe as All For One and Shigaraki are targeting him to get their hands on One For All.
- In the flashback Midoriya sees in the vestiges of One For All, Midoriya witnesses All For One transfer a Quirk from a man who doesn't want it because it makes it look grotesque to a man who needs it for self-defense. Both men go through with the transfer despite All For One's brother Yoichi's warnings and agree to help All For One should he need it. Chapter 336 reveals that Yuga Aoyama's parents got him to give Yuga his Quirk, resulting in Yuga getting a Quirk that was incompatible with his body and the family being blackmailed into doing All or One's bidding, showing just how awful it is to get "help" from All For One.
- Almost every moment of Aoyama's antics after he's revealed to be the UA Traitor, particularly when you realize that his supposedly self-centered actions have been his attempts to sabotage himself on purpose. He draws attention to how he was nowhere to be seen in the USJ but is only able to mention it to Tsuyu, tries to sabotage his possibility of attending the Training Camp to avoid having to sell out its location by embarrassing Uraraka by asking her about her crush on Midoriya during the practical exam as well as purposefully doing poorly on the written exam (only beating Ashido and Kaminari), hides away from view when the villains' attack again and is visibly terrified at the idea of attacking Dabi, attempts to fail the Licensing Exam and is only able to pass because of everyone else's sudden appearance. He's been all but screaming that he's the traitor, but nobody's bothered to care.
- Aoyama's odd tokens to friendship towards Midoriya also serve as this. His excuse of them both having quirks not suited for their bodies takes a new light when you realize he probably thought that Midoriya was another plant by All For One, given how recently he gained his quirk and how he's so inexperienced with it. Seeing him spontaneously manifest Blackwhip just served as fuel for the fire. His pointing out how similar they were could have also been another attempt by him to weed out the traitors — he was already trying to signal how he was a traitor to everyone and was trying to also implicate Midoriya by connecting them, to both remove another one of All For One's moles, as well as potentially remove Midoriya from All For One's grasp.
- Aoyama's defeat at the U.A. Sports Festival comes after his belt is destroyed. It's a lot harder to laugh at after it's revealed that he suffers from a condition where his body can't handle his own Quirk without it, and said condition also causes occasional Power Incontinence.
- The omake where Mt. Lady makes fun of Midnight by calling her old is Played for Laughs, especially when the argument devolves into a Cat Fight. It becomes a lot less funnier when Midnight dies at a very young age (at most in her early 30s) in the Paranormal Liberation War.
- Iida's brother Tensei/Ingenium gets crippled for life by Stain, a Hero Killer who specifically hunts heroes he believes are greedy and/or corrupt. In Season 3 of The Boys (2019), A-Train (the main speedster in this series) hosts a town hall meeting where his brother Reggie is crippled for life by Blue Hawk, a racist Dirty Cop who is a superhero in name only.
