Hello fellow readers and writers, I am sure everyone is aware of Izuku's new demeanor in the recent issues of My Hero Academia. With him being more aggressive and acting more as an Antihero like venom, Deadpool than a generic hero or like All Might, or like the more colder but still kind hearted heroes like Batman.

Though I may have come up with a theory regarding this new side of Izuku. If anyone remembers One for All is the combination of a quirk that allows the user to transfer it to another person and a quirk to stockpile energy. Which grants One for All the unique capability to grow in power with every new user who inherits it. However as we have seen Izuku also gains the quirks of all the previous users such as Float, Black Whip, Danger Sense, Smoke Screen and Fa Jin.

With all the collective consciousnesses of the previous users, as was shown when Izu unlocked Black Whip, he was inside his mind scape and Black Whip's original user Daigoro Banjoro had introduced himself to Izuku and explained his quirk to him. That said, I theorize that it would be possible for the previous consciousnesses to influence Izuku in some way or other. Such as affecting his personality or fighting style as he trains with his abilities allowing them to grow stronger.

However this also means that it can have a negative side effect, if the wrong user's consciousness could possibly be awakened they could have been the cause of Midoriya's new cold and distant personality. I'm pretty sure someone may be poking holes on my theory saying "but if your theory is right which of the previous holders of One For All could have done so and if so why would they be so negative?"

Well, it's not the previous holders of one for all, at least not after it's creation. Remember what I mentioned earlier about this quirk being a combination of two quirks? Transfer Power and Stockpile Energy?

Taking into account of the information made above, One for All can be transferred to other users, grow in strength over time, carry the quirks of previous users and carry their consciousness. Now answer this, who had existed around One for All's creation and it's time gathering net strength and power? Who had a quirk that was included in it's history? Who's known to be extremely cold and aggressive? Who has a similar resentment Izuku currently has towards other heroes? And who has such a negative and nearly malicious mentality to effect someone this way?

Taking these factors into account

- Existed in some time during start or middle of One For All's History

- has a quirk included in One For All

- Has a very Negative Influence

Also think about this

- who is comfortable with turning a distraught youth into a tool for their own personal gains?

ALL FOR ONE!!!!!

That's right, All for One fits multiple factors, he had a hand in creating One for All in the first place. He gave his younger brother, the original holder of One for All, the Stockpile quirk which turned it into what it is now. As as said One for All carries on the consciousness of its previous users, and as demonstrated with All for One the quirks he can pass on still retain the generic traits of the holders they came from. As said with the original Nomu during the USJ Arc, he was originally someone else and carried the DNA of other individuals.

And while the stockpiling quirk had come from someone else, not All For One himself, it still stands to reason that All for One's DNA and consciousness could have still found it's way into its rival quirk through the transference and creation. That being said, All for One's presence alone in Izuku's quirk is more than enough to trigger the shift in his personality. As to why it hasn't happened to the other users of One for All, there are three factors in this. One is the strength, at the time All for One's presence in the previous users was at the same strength as the quirk itself. Starting out relatively weak, however over time it may have been waiting, growing in strength until it had enough of it to influence the Change in the current user. The second factor, something had to have triggered the possible remnants of All for One during the time period of Izuku's recent battle and his turn to the dark side.

And the third, something All for One has shown before with Shigiraki, he could have been trying to find a weaknesses in the psyche of the users, some form of mental or emotional instability to exploit. Shigiraki had a lot since he was the cause of his mother and sister's death accidentally and killed his abusive farther. With Izuku, as much as we want to deny it, he also has a form of emotional instability. Being initially quirkless he was bullied, ridiculed and tormented for nearly a decade which should undoubtedly leave several emotions scars.

Though because of Izuku's still heroic nature and kind heart, he only uses his powers to help others and never against the innocent. Which limits All for One's possible influence on him, as for why All Might wasn't affected since he was quirkless, his physical abilities at the time when acquiring One for All allowed him to dispatch All for One quicker so it wasn't able to set in.

Again this is a theory but please vote, comment or both if you think this could be legit.

And please, feel free to make suggestions on your own theories.