Warning: Spoilers for My Hero Academia Season 6, Episode 15While it's long been clear in My Hero Academia that Deku and All for One have no choice but to fight each other, never has this fact been more succinctly summed up than it was by All for One's dialog in the new episode, "Tartarus."
All for One was arrested after All Might's final battle with him in My Hero Academia and has been deep inside the Tartarus prison ever since. Despite that fact, All for One's machinations have continued moving in the outside world, and with Shigaraki now awake, the time has finally arrived for All for One to free himself. Using Shigaraki, he mounts an overwhelming attack on the prison, freeing as many prisoners as they can to cause additional chaos across Japan. As All for One looks out over the devastation that only marks the beginning of his new rise, he utters a very interesting line of dialog to Shigaraki.
All for One says that, "this is the story of how I become the greatest demon lord." The wording here is very deliberate, echoing the statement made at the beginning of many episodes of My Hero Academia. In the openings of My Hero Academia, Deku will often say, "this is the story of how I became the greatest hero." The only difference between the lines, aside from hero and demon lord, is the tense; otherwise, they're exactly the same. Having All for One use this exact same phrasing emphasizes both the similarities and differences between Deku and All for One, and both sentences perfectly explain why the two must fight.
The Goals of All for One and Deku
All for One may be an adult, but his motivation, that which pushes him to achieve his goals, is actually about as childish as it gets. In flashbacks with the First User (and All for One's brother), All for One expressed that his inspiration was the comic books he used to read as a child, back in the days before Quirks. All for One admired the villain, who was apparently quite successful in the early volumes of the comic, because he took action to make his desires real. Deku, on the other hand, grew up idolizing All Might and heroes in general; he's wanted to save people, not to earn their praise or for fame or rewards, but just for the sake of reducing their suffering. Deku is still young, so it makes sense for him to have such a dream, but All for One? Not so much. If Deku were to read the same comic, no doubt he would relate to the hero in much the same way All for One did with the villain. Not only are their goals opposed, but their very inspirations come from the same source, pushing them in different directions. Deku and All for One were destined for conflict, perhaps even before inheriting One for All.
Deku and All for One may be fated rivals, but as things stand neither is ready for their final battle. As My Hero Academia's greatest hero and demon lord prepare for that day, only time will tell which one of those titles will be proven true.
My Hero Academia streams new episodes on Crunchyroll every Saturday.