My Hero Academia tells the story of young Izuku Midoriya's journey to become the greatest superhero, Deku, just like his idol All Might, the no. 1 pro hero in the world. Since being selected by All Might to become the inheritor of his great superpower, One For All, Izuku and All Might have become an inseparable pair, as the older hero mentors his successor. However, the writing has been written all the wall ever since My Hero Academia started, that this series is going to throw a major moment of tragedy fans way, eventually. It's pretty much inevitable: All Might must die, so that Deku can become the best hero.
The notion that All Might will, and must, die isn't something that's purely opinion, it's actually something already loaded into the My Hero Academia mythos: All Might's all-powerful One For All quirk carries a very tragic history with it. The anime has already touched on the issue several times, and the most recent manga arc has gone even deeper into the matter. Without dropping any big spoilers, we now know that a defining quality of One For All is the tradition of its users all tragically dying by the hand of series big bad, All For One, who is the evil opposite of One For All. In fact, one of the biggest discoveries Deku and All Might have made is that the power's function is determined by the manner of succession in users:
- Many former One For All users received the power from a wielder who was dying, and passed it on as a final act to whomever was nearest. Those users could not access the full scope of the superpower.
- A few users (like All Might and Deku) were personally selected to receive the power (because of character), and gain access to the full power set.
Even when One For All was voluntarily passed on to a "chosen one," the former user ends up being murdered by All For One - just like All Might's mentor, Nana Shimura, was. That extensive backstory forms a very clear and undeniable pattern, you'd be blind not to see: there isn't really room for two One For All users to stick around in the world for very long.
Now, some My Hero Academia fans may argue that a big part of Izuku Midoriya's story of becoming the greatest hero could be having Deku finally break the cycle of death and loss by keeping All Might alive and defeating All For One. It's a fair argument (one while explore in detail, soon) but there are a couple of clear objections to those notions in the series:
- All Might's alter-ego Toshinori Yagi has basically been slowly dying since the series began. All Might's first big win over All For One left his body horribly and seemingly incurably injured.
- My Hero Academia has already seen tragic loss around Deku (Mirio, Sir Nighteye).
With a major war now underway in the My Hero Academia manga, it doesn't seem like Deku's story is about to somehow get less tragic- nor should it. War brings significant loss, and for Deku, the kids of U.A., and the pro hero world, this current war with the combined efforts of The League of Villains and Meta Liberation Front army must end with scars that will never fade. The death of the Pro Hero Symbol of Peace - especially with Toshinori going out with one last heroic (non-powered) act - seems like destiny.
...at least based on everything My Hero Academia has told us, thusfar.