WARNING: This page is meant to describe events as they related to much later, very significant ones. Thus this page will have no spoiler marks at all. You Have Been Warned.
- While All Might explains the nature of "One For All" as a Quirk that is to be cultivated and inherited, there are eight balls of light that are interconnected, like a constellation. These hint at the eight previous holders of the Quirk, with Midoriya being the ninth successor.
- All Might explains that One For All cannot be stolen. Though it seems that this statement should be normal given that it is a Quirk that is transferred between people, this becomes an important clue later on when All For One shows up.
- The vestiges of One For All show up when Midoriya is battling Shinso, and break his finger to snap him out of Shinso's brainwashing. This not only foreshadows Midoriya's eventual alliance with them but also foreshadows All For One (from whom One For All was given), being the sole possessor of the Quirk before Shigaraki, eventually strengthening the connection to pull a Grand Theft Me on him.
- All Might gives Midoriya a training regime to prepare him for U.A. Midoriya quickly starts going beyond the limits the plan called for, causing him problems with overwork. Not only does Midoriya hurting himself from pushing himself too far become a recurring element of the series, but the differences between his and All Might's personalities seriously hamper their teacher-student relationship.
- Early in the USJ Arc, Kirishima describes his Quirk as not at all "flashy" and thinks it would be easier for him to be a pro hero if he had a flashier moniker. Come the Work Study Arc, it's revealed that during middle school, around the time Bakugo and Midoriya fought the Sludge Villain, Kirishima was having self-doubts about his chances at being a hero, even giving up on going to U.A. at one point.
- In the opening shots of the second opening, Midoriya can clearly be seen. Note the sleeves on his arms, which seem to have been torn off. This is a hint of the permanent damage he'll do to his arms at the end of the arc.
- All Might mentions One For All boosts a person's Quirk greatly. This comes into play when Deku unlocks the powers of the other users, they're all amplified as All Might said.
- During the last thirty-seconds of the third opening, one gets a decent shot at all the major members of the League of Villains, including its real leader, as the shadow behind them heavily resembles All For One.
- During the Remedial Course Arc, an In-Universe theory called the "Quirk Singularity" is introduced. Later on, during the Joint Training Arc, it's revealed that One For All is a perfect example of this theory, having grown strong enough in power over the first eight generations to allow the ninth wielder, Midoriya, to not just interact with the "ghosts" of his predecessors, but also allow him access to their Quirks. Although that means Midoriya will be more powerful than all of his predecessors by far, it also means he'll have an even more difficult time mastering One For All than initially thought.
- In the climax of the first volume of the light novels, when a villain takes Class 1-A's parents hostage, who are visiting for Parents' Day, Inko Midoriya calms down a belligerent Mitsuki Bakugo by telling her, "We're hostages, remember?" This sounds like Inko's trying to remind Mitsuki of the danger they're in, but it turns out to be a warning not to break character, as the entire thing is just an exercise.
- All Might explains that One For All is passed down from each generation to the next while accumulating power with each generation adding to it. All Might himself also stated that he instantly mastered One For All while stating why it can be hard for him to teach Midoriya. Later, when Midoriya starts to see the vestiges of the previous One For All users, they have a life of their own and aren't just memories or remnants. This is a major hint that not only does One For All gain power for each successive generation but also gains the Quirks of the holders of One For All. Now that One For All has become strong enough, not only can the vestiges communicate with the current wielder, but they can also lend them their powers. All Might missed the previous Quirk users because he was an Instant Expert with the Quirk and never bothered much to master it completely, missing the advice the former Quirk Users could have given him.
- Aoyama is conspicuously missing when the League of Villains attack the USJ, foreshadowing his role as the traitor for the villains. Similarly, Aoyama's growing interest in Midoriya when noting the difficulty Midoriya is exerting in trying to control One For All is a hint that Aoyama himself was also born Quirkless, and similarly has a great difficulty mastering Navel Laser, and he thought Midoriya also got his Quirk from All For One.
- The cover image for Chapter 306 has Midoriya and Shigaraki sitting atop a pile of broken TVs, each holding a monitor that displays the other's mentor figure, All For One for Midoriya and All Might for Shigaraki. By the time of the Final Battle, both characters wind up taking characteristics of their opposing mentor into their fighting style, essentially becoming a good/evil version of them on the opposing side of the fight, with One For All having evolved enough to allow Midoriya to wield the Quirks of the past users in tandem with the Super-Strength function like a weaker version of All For One's signature ability, and Shigaraki having grown so powerful after being enhanced by Garaki's research and gaining All For One's Quirk with its accumulated power that the only reason the heroes have a chance is by using Erasure to seal his multitude of Quirks, leaving him with only the base strength of his enhanced body to fight with, which Shigaraki regularly compares to All Might in terms to illustrate to the heroes how unstoppable he is even without his Quirks.
- In Chapter 334, as the vestige of Star and Stripe fades away, having burned itself out from destroying so many of All For One's stockpiled Quirks, it taunts the shredded and tattered mental amalgamation of Shigaraki and All For One that one day a true hero will put an end to him and his ambitions. Whilst the All For One aspect of the avatar spitefully denies her claims, it's shown that within a hole in the avatar's figure made by Star's assault, a mental version of "Tenko Shimura" resides at the center, responding to Star's words and uttering Midoriya's name. During the Final Battle, it's revealed that this is all that remains of Shigaraki's good half, being brought to the surface in denial of Mirio's claims that Shigaraki suffered from a Friendless Background. As All For One only understands negative emotions like anger and hatred, he was able to assimilate the "Shigaraki" aspect of his psyche, whom he specifically groomed since childhood to be as hate-filled and misanthropic as possible, but was completely blind to the part of Shigaraki's mind that still embraced the few happy memories he possessed, leaving him mistakenly thinking he'd assumed full control over Shigaraki's mind and body.
- Several examples related to All For One:
- During the vestige vision Izuku receives upon beginning to pass the singularity with One For All, Yoichi is seen futility attempting to prevent his brother from preforming a quirk transfer between a quirkless person and a Quirk-user whose mutation has warped his appearance and lead to him offering Fantastic Racism, warning the two that taking his offer would be nothing but harmful for them in the long run. It's later shown that taking a similar deal was how All For One was able to create the U.A. traitor, a fact they very much regret by the present time.
- His inability to comprehend altruism, on full display during his battle with All Might in Kamino Ward, plays into the later reveal that his psychopathic nature handicaps his ability to steal One For All. As he can't understand what it's like to care for something beyond your own wellbeing, he cannot grow as a character, and thus has remained the exact same Card-Carrying Jerkass for generations. This is why One For All can't be assimilated by his Power Parasite abilities, as it is comprised of people whose collective Heroic Willpower are too strong for him to ever overcome without a strong emotion like Shigaraki's hatred.
- He waxes lyrical to the immobile Izuku and Nana Shimura when they briefly meet inside the vestige realm during his first attempted absorption of One For All, mentioning his own experiences with the vestiges of his former victims and how they were antagonistic towards him in his dreams until he passed the associated quirk to another. This antagonism comes to the fore during his battle with Team Endeavor, as Jiro's defiance of him and resolve to fight regardless of his power succeed in motivating all the vestiges stored within himself to rebel against him as one, leaving him vulnerable at a crucial moment and allowing the heroes to badly damage his life-support mask before he regains control.
- When All Might first talks about him, he brings up how he's Shrouded in Myth and the only knowledge about his existence as Japan's past Shadow Dictator is rumors on the internet, emphasizing his unseen menace brought back by his re-introduction into the present narrative. All Might even admits that he didn't talk about him before because he thought he'd dealt with him for good and didn't see any reason to burden Izuku with the knowledge then. During the Final Battle, this gets thrown back in All For One's face to his detriment: far from his monstrous villainy making him a feared villain who terrorizes everyone and will be remembered forever in infamy, it just means that nobody wants to remember him or talk about him, and history books have intentionally ignored any recollection of him while retaining the relevant lessons from the Dark Age of Quirks, dooming All For One to being a non-entity in the grand scheme of history.
- Eri accidentally rewound her father out of existence, which drew the attention of the Yakuza and the League of Villains. After a long chain of events, All For One meets a similar end after overusing Rewind to spite All Might and Bakugo.
- There were numerous hints leading up to the reveal of the Awful Truth that All For One engineered Tenko's Dark and Troubled Past, indirectly enabling his childhood trauma as a means of isolating and manipulating him for his plans and as a means of mocking Nana and All Might's efforts as heroes in opposition to him]].
- Kotaro notes that Tenko has not shown signs of having a Quirk even at five years old, and Izuku later discovers that those who naturally possess a Quirk cannot gain a second Quirk without severe side-effects — in the case of the holders of One For All, they suffered from Rapid Aging, with only the Quirkless All Might and Izuku immune to this. Despite this, and his goal being to become an immortal Demon Lord, All For One gives Tomura his original Quirk with all its stockpiled Combo Platter Powers, implying he believes Tomura will be unaffected from any negative consequences of possessing more powers than he was 'naturally' gifted with. It later transpires that Tenko did have a natural-born Quirk, which all For One stole when he was a baby as part of his plan, meaning he is actually unaware of the negative long-term consequences of possessing more powers than one is meant to naturally hold.
- Tomura's Quirk itself bears no resemblance to anything seen in his family lineage. Eri's example shows that it is possible for mutant Quirks to unexpectedly manifest in children, but in her case everything learned about it and its effects was done by guesswork and experimentation, and even by the present time the heroes aren't fully certain if her Rewind is even the primary effect of her Quirk. However, All For One and Garaki seem quite confident when explaining Tomura's Quirk, and even certain that it is linked to Tenko's hatred, implying they're far more familiar with the 'new' Quirk than the boy whom it manifested in. Decay is later revealed to be a deliberately-modified version of Overhaul's Quirk, missing the Required Secondary Powers ability to restore what it destroys, which in turn ties into All For One's Control Freak tendencies towards Yoichi, whom he'd groomed Tomura into a reflection of — having lost his Twin to somebody's "saving hand", he granted his intended vessel a Quirk designed to destroy anyone who did the same, with Izuku indeed having to endure decay destroying his vestiges arms in order to quell Tomura's hatred within his Mental World.
- Despite the extensive damage Tomura's Quirk caused when he decayed his family home, and the death of an entire family overnight, no police or heroes responded to the crisis, and no records were made afterwards; nobody seems to have alerted the authorities when Tenko was staggering around covered in blood. All For One was able to appear before him when he felt most abandoned, and recovered the bodies from the rubble to fashion their remains into Tomura's Companion Cube. All For One even knew who Tenko was when he found him. Garaki later reveals that All For One made a point of locating 'twisted, warped seeds' that could serve his purposes, and appeared before them as a saviour to gain their trust, as shown with Touya Todoroki's self-immolation, implying Tenko's situation was more calculated than he realised.
- The flashback of Yoichi's death shows that he was blown apart into bloody chunks by his sibling, leaving only his severed hand which was then preserved as a twisted memento. The parallels to Tenko's own traumatic Quirk awakening and All For One's efforts in grooming him to intentionally resemble an evil mirror of Yoichi greatly imply he may have intentionally recreated his own experience with Tenko, as "proof" that his chosen vessel for his essence was "born twisted" like himself, and thus capable of committing such an act under similar circumstances.
- When Tomura has a Troubled Childhood Flashback to his Traumatic Super Power Awakening when fighting Re-Destro, there's a seemingly-innocuous panel of Tomura being dropped off at his house by what appears to be a neighbour, shortly before Tenko's Quirk starts manifesting itself for the first time. The man's silhouette bears a resemblance to All For One's appearance when he rescued Toya. When successfully inflicting mental damage against Tomura by exploiting their Psychic Link between the twin Quirks they inherited, it causes a merging of their memories as distorted visions of those they've seen and met appear around them. After injecting enough damage to cause a deeper interlink, Izuku sees a vision of a young, black-haired Tenko prior to his family massacre, walking with his hand held by a man in a suit, similar to All For One's past appearance, taking noticeable notice of it amongst the others. Another memory he encounters when trying to enter Tomura's mental core is nearly getting hit by a speeding truck driver, who yells at the "kid" to go home to his parents instead of loitering on the street. It's shortly thereafter revealed that these events are all tied to All For One's initial transfer of Decay to Tenko, having approached him after the near-miss to escort him hm and transferring Decay through their hand contact.
- The visions relating to the Awful Truth becoming more prominent the more damage Izuku does to Tomura also counts as Five-Second Foreshadowing that the Vestige of All For One is Not Quite Dead, and is trying to reveal these facts to his Superior Successor in order to break his will and leave him in full control of the body.
