WARNING: The following contains spoilers for Season 4 of Attack on Titan, now streaming on Crunchyroll Funimation, Amazon Prime and Hulu.
Attack on Titan's shonen hero has always been Eren Yeager, the hotheaded boy who lost his mother when the dreaded Titans stormed the wall protecting Shiganshina one fateful day. Ever since then, Eren has taken control of his own destiny, or at least tried to, and in Season 4, he is an essential guardian of Paradis Island and its Eldian inhabitants. Or is he its biggest villain?
This dark action series has had more than a few antiheroes and bittersweet moments, such as the brutal but brave Captain Levi and the conflicted Historia Reiss (who has since taken the crown). But by now, Eren has amasssed more power than ever, and that, combined with his ruthless ambition, makes him a startling parallel to My Hero Academia's supervillain, All For One (named after his greedy Quirk).
Power Is Always Justified In Eren's Eyes
Eren Yeager's path to power began on the day the Titans arrived, a day on which he felt agonizingly helpless as the Pure Titan of Dina Fritz (Zeke's mother) ate Carla Yeager (Eren's mother). After that, Eren channeled this frustration into his soldier training. Then his true powers awakened, the mighty Attack Titan during Season 1's battle of Trost, and once Eren was accepted for what he was, a Titan Shifter, he began practicing with that incredible power and recklessly pursued his enemies. He challenged Annie's Female Titan and Reiner's Armored Titan, and eventually, Paradis Island became free of its enemies, allowing Eren to learn the truth about the Marley Empire. But he was just getting started, and he sought yet more power.
When the three Marley Warriors broke Wall Maria, everyone lost, and vengeance was on everyone's mind as a consequence. No one could blame Eren for his seething rage and longing to wipe out the Titans, though Mikasa was rightly concerned about Eren's reckless streak and borderline self-destructive ways. At first, Eren's shonen power-scaling in Attack on Titan followed the tried-and-true formula, but in Season 4 he's decided to kick things into the next gear, which is when his path to villainy truly began. He needs it all: more Titan powers, more powerhouse allies, more opportunities to strike his enemies, and anything else he can get.
Eren is now three Titans in one, including the ultra-important Founding Titan, and he's flaunting that power every chance he gets. As of the time of this writing, Eren is in a jail cell, but he's only humoring his jailers. With his new War Hammer Titan power, he can reshape matter around him and escape from any prison or vault, something he uses to intimidate Hange Zoe with. Eren is ready to strike at Marley once again with his many powers, and that, combined with the Rumbling, should suffice for him. Meanwhile, Armin, Mikasa, Connie, Jean and the others are terrified at what Eren has become: an armada of power in one young man.
Eren Has Become A One-Man Army, Like All For One
All this makes Eren a startling mirror of All For One, with the main difference being that Eren started off as a hero, while All For One was a villain all along. All For One's power-hoarding Quirk functions in a similar manner to the way Eren has been expanding his Shifter arsenal, too. As of Season 4, their mindsets are parallel, as well. Like Eren, All For One believes that power is always justified -- that the ends justify the means. It's a dog-eat-dog world, according to both characters, and power is the only language that their enemies speak. Eren and All For One have had no qualms with seizing extra power if it gets them what they want, and if their friends don't like it, then those friends had better get out of the way. They don't wonder "How can I do the right thing?" What they really think is "How can I accomplish anything I want?" Their allies and enemies soon learn to fear and admire them alike.
It may also be added that All For One is more of a legacy than a person, and the original All For One is perfectly willing to pass the torch to Tomura Shigaraki to continue his villainy. Similarly, Eren wishes to pass on the Founding and Attack Titans on, not for the sake of peace but to keep the world scared of Eldia's power. Similarly, Eren can only be a Titan Shifter for so long, but his vengeful, radical pro-Eldian mission may continue with his heir, whoever that ends up being. Ideally (for him), it'll be someone who's also a pro-Eldia radical, and become the Tomura Shigaraki to Eren's All For One.
Eren is rapidly alienating his allies and fellow Eldians (aside from Historia and Zeke), and it's fair to say that he's becoming a loose cannon with far too much firepower at his disposal. But without power, Eren and All For One would say, nothing is possible, and that is unacceptable. Both characters have big ambitions for the world and they'll stockpile as many powers as they must to unlock their dreams, whether people like it or not.