WARNING: The following contains spoilers for Season 4, Episodes 5-6 of Attack on Titan, "Declaration of War" and "The War Hammer Titan," now streaming on Crunchyroll, Funimation, Amazon Prime and Hulu, as well some minor spoilers for the Attack on Titan manga.
The Attack Titan, once a mysterious and feared beast within Paradis Island's walls, has grown to become the Attack on Titan anime's biggest rebel heroes, both literally and figuratively. Season 4, however, is leading its host, Eren Jaeger, down a darker path than ever before, stripping away his youthful idealism and raw angst to leave him a calm and strangely complacent husk of his former self during the attack on Marley. But it's not just Eren we should be worried about. The Attack Titan itself could well be harboring dark desires of its own. In fact, it might just be a manifestation of the Devil.
Even on the surface, it's hard not to see a similarity between the Attack Titan's facial features and the "Devil of all Earth" from Eldian mythology -- the horned creature, as depicted in Eldian drawings, that passed the power of the Titans to Ymir Fritz 2,000 years ago. Ymir went on to become the 'mother' of the Nine Shifters, as well as the Titan curse carried in each and every one of her "Subjects" from then on. Studio MAPPA's version of the Titan makes the similarity all the more apparent, with the creature's bloodied, snarling mouth and pointed ears made a terrifying focal point of Episode 6's preview. This isn't to say that the Attack Titan is the Devil incarnate, but it could well be the clearest representation of the Devil's will on Earth.
It's worth noting that the Attack Titan's previous holder, Eren Kruger disputed the validity of this creature's devilish qualities, asserting that its evil nature is just anti-Eldian propaganda (which is very plausible given that Eldians are offensively referred to as "devils" themselves). There's some suggestion in the manga, too (without going into heavy spoilers) that the tree Ymir fell into and died within was actually the thing responsible for giving her the power of the Titans -- and is even the possible progenitor of life itself in Attack on Titan's world. The Norse Tree of Life, Yggdrasil, in other words; which is supported by its ability to alter the genetic makeup of an entire race of people.
But Grisha Jaeger, the man Kruger chose as his successor, pointed out everything that is known about the Devil of All Earth and Ymir, including the former's name, comes from Eldian-made stories. It's hard to imagine, too, that beings as hulking as Titans could have been given to humans for any other purpose than domination, which is exactly how the Eldians used Ymir to build their empire centuries ago; something that a demonic presence seems more likey to influence.
Other evidence to support the connection between the Attack Titan and the Devil also comes from Eren's own words. His constant assertion that he needs to "move forward," no matter the cost, taps into the unanswered question of what the line is between Shifter Titans and their hosts, and what the true role of the Attack Titan really is. Given that the Titans' founder got her power from this supposed Devil -- powers that were disseminated between the Nine Shifters -- and each host has access to past hosts' memories, there's an argument to be made that each of them holds a piece of her will within them, and possibly by extension, this Devil's will. The 13 years to live thing aside, if true, this may be the most 'cursed' thing about the Titans.
The Attack Titan, however, is even more unique among the Nine. It's supposedly immune to the "self-righteousness of the king" who bound the Founding Titan, and more importantly, perhaps, it has future memory sight, evidenced by Eren Kruger knowing Armin and Mikasa's names years before they were even born. It's this ability that likely drives its need to "move forward," a drive that is clearly imprinted into the subconscious of all who inherit it. After 100 years of inactivity, how else do we explain the Founding Titan falling into the hands of the only person with the means and potential desire to use it, beyond mere plot contrivance?
Think back to the anime's first episode title: "To You, 2,000 Years From Now." There's a clear line drawn from Ymir to Eren, there. The Attack Titan has been steadily making its way to Eren Jeager all this time, knowing that he'd be the one to move it to its eventual target. The question then becomes, what is that target, exactly?
Eldian myth states that Ymir made a deal with the being for power and freedom but usually when you make a deal with the Devil, the Devil expects something back. Well, Attack on Titan's Norse mythology roots makes it pretty clear that the Rumbling the Founding Titan has the power to enact -- a world-ending catastrophe -- is its version of Ragnarok.
Throwing this Devil's deal into the mix for a little Biblical flavor, we could theorize that what the Devil wants out of its end of the bargain is nothing short of the end of the world -- and Ymir, at the time, had the rage and reason to agree to make it happen until her premature death. The Attack Titan, therefore, which can only "move forward" and has access -- uniquely -- to both past and future history, is the only Titan capable of pushing the world towards this apocalypse.
For this reason, the Attack Titan, not the Founding Titan, could even be considered the most important Titan of them all, as the preeminent agent for facilitating this apocalyptic promise being carried out, as well as the most obvious personification of the Eldian Devil, even if on a purely symbolic level. The Founding Titan might be the one to give the order to begin the end of the world, but it's the Attack Titan that has the power to operate outside of history, changing it as it sees fit.
This all makes Eren look like the most dangerous man in the world right now, even if he's unaware of the will of the beast from below that might be lurking inside him. Attack on Titan fans will just have to nervously watch and find out whether or not the shonen protagonist is fated for a titanic fall from grace.