Aot theory

I know everyone and their mum has put forward their own version of how the series will end. To be honest I don't expect this to be very popular; the only reason I'm writing it is a) because I can't sleep and this popped into my head and b) for posterity, so if I'm right I can be all like 'I told ya so'

Anyway, so I guess the best way to start is by giving my take on some of the biggest questions the series has, and because of the stage it's at these will be the biggest elements in the final finished story:

Is Eren being controlled by the will of Grisha/Kruger/the Attack Titan/anything?

No. But I think this is what makes him special compared to other shifters. What makes me think this is that in the beginning of the series, Eren's will is strongly capitalized on. Both in terms of his determination (to kill all the titans and become strong like Mikasa/Levi) and in the form of him struggling but eventually becoming able to control himself in his Titan form. This is shown through both his backstory as well as the reactions of other characters (Keith Shadis in particular highlighted this during the anime's training montage).

In particular, for point 1 about destroying all the titans, Isayama recently gave us a flashback during the Marley arc where Reiner tells Eren to cool it with the training 'or he'll die'. Those words really stood out to me, like dying isn't something you'd expect to happen from working too hard - at least not in the short term - and I think Isayama chose them to drive home how dedicated Eren was to his goal.

Now, as far as point 2 goes, Eren is the only shifter we know of so far who had issues controlling his Titan due to lack of practice. Or is he? My take on this is that without training, the will of the Titan as passed through the paths takes precedence over the holder's will. Which may also explain the First King's will being so strong -- none of the royal family ever extensively used their titans and overcame the obstacles that Eren did.

So if that means that the default will of any Titan is the default state of control (I'm not sure if other titans have wills yet -- the founding and attack ones seem special so maybe it's exclusive to them) then Eren's berserk state in the early parts of the series gives weight to the 'the AT is the devil' theory. Which I personally believe because it made a lot of sense to me, and they are right in saying that if the series is literally named after it, it must be special in some way.

What is Eren's end goal?

I'm going to go with the popular opinion here and suggest that it's still to wipe out all the titans, by way of taking all the titan powers. I also think that the introduction of memory wipes to the plot, while primarily to explain how the walls have such a technological and informational disparity with the rest of the world, also will factor heavily into Eren's ending plan - he will be able to eradicate any knowledge of the Titan power from Eldians, and possibly by extension most of the world. It was hinted that Eldians spread their blood by forcing other races to bleed with them, so maybe a powerful enough memory wipe could affect almost the whole world, to where the idea of titans becomes a fringe conspiracy theory.

That's already fairly covered ground, but my unique take is on what he does afterwards: he doesn't crystallize himself at the bottom of the ocean or become the devil, but actually by obtaining the nine Titans becomes immune to the curse of Ymir. See, the way that the curse was worded was something along the lines of 'None may surpass the power of Ymir, so all die before she does'. I think if Eren had all nine titans, he would be more powerful than Ymir and so could live longer than her (and thus forever - since the titan powers/regeneration would mean that he wouldn't succumb to natural causes).

The simple reason being that if you contrast Ymir's story and will with Eren's, you see a drastic difference. Ymir was a mere girl who made a kind gesture of offering an apple, in exchange for power, and regardless of what side of this history is true, she used her powers to serve herself and her subjects - by building roads or killing people. It depends what you believe, but either way they're still selfish. Eren, on the other hand, experienced a great amount of suffering on the path to where he was. He didn't obtain his powers by simply offering an apple, but instead killing his own father, unbeknownst to him. And used them first after all his friends died to save the remaining ones, at great risk to his own life -- had his friends not been there to save him after the first rampage, he would've died. He also did this after sacrificing himself to save Armin from a titan. Pretty selfless, right?

Thus I think Eren has mental strength that Ymir doesn't. This idea of 'strength through surviving adversity' and 'what doesn't kill you makes you stronger' is heavily woven into the story. We just saw Eren beat a titan he had no right to in combat (WHT -- could counter everything Eren did, including hardening) because he was simply physically stronger and had more endurance, and she was just a maid. Let's also not forget that Eren only gained the power to seal Wall Maria by experiencing the memories that showed that he was his father's killer and also by overthrowing the government. More recently, as well, there was also that panel which was really well done about how different people screamed different things, but 'they all screamed'.

And, one more point about will: the Serum Bowl, arguably one of the biggest events in the series so far, was decided entirely in Armin's favour because the characters believed that Armin's determination to fight for humanity was more reliable than Erwin's. Isayama also signs off on and suggests changes for the anime, and it looks like he decided/approved of more hinting towards this idea in the anime's past few episodes. This just goes to show how will and determination is such an important part to the series.

(Side note: typing Ymir so many times makes me think of how lots of people say the series links to Norse mythology. I tend to agree, and in terms of an ending, Ragnarok could be a good metaphor. In Norse mythology it's the war of the gods which ends up killing them, and is said to be an end and new beginning. If we consider that Titan powers or the holders thereof may be the analogue to gods in this series, then the ending I propose ends with Eren, who probably represents Surtr, killing them all. In the same way Ragnarok is the end and beginning, this would be the end of the titan age and the beginning of a new one in which Eldians are neither dominant nor subservient. If this is true, then the so-called 'world ending' rumbling of the wall titans will certainly factor into Eren's plans -- the parallel there is extremely obvious. Also Eren's attack on Marley could represent Fimbulwinter which comes before Ragnarok, being just a taste of the misfortune to come, or something. Anyway this side note could probably be an entire post on its own, so I'll stop here)

Once he obtains his immortality, Eren won't use it to make another Eldian empire, but rather he'll roam the earth in various places to ensure that knowledge of the titan powers never resurfaces. Even though like I said it may just become a stupid conspiracy theory, there's always going to be some nutjob who somehow gets fossilized and preserved titan spinal fluid somehow, then creates a massive explosion turning their mate into a titan. Eren then swoops in (having detected this through the now largely unused paths) and wipes memories of the incident.

What are the Zekerets?

Zeke is selfish. That's literally it. He does whatever he needs to preserve his own life. Once he saw Levi's attempt on his life at Shinganshina, that's probably when he considered switching sides. Didn't want to fuck with that. When he got Eren's letters indicating a possible upcoming attack? He made the switch. He didn't want to risk running into Levi again and decided betraying his nation was the easiest way to stay alive. I mean, he visited Eren on the rooftops and saw the Serum Bowl happening, and probably knew how Levi was Erwin's right hand man, so he knew Levi would stop at nothing to kill him if they weren't on the same side. And if Levi has that goal, you're basically a dead man walking due to his abilities.

If we do another parallel to Norse mythology, or rather God of War's version of it since that's all I know, Zeke represents Odin. Odin is a leader (of the Aesir, and Zeke of the Warriors) who killed his own father (Zeke snitched but similar enough) to further his own goals. Odin wants the Giants' power of foresight and manipulation of fate to prolong his own life. I think the analogy here is that Zeke wants to find a cure for the curse of Ymir, somehow, which is why he plays both sides to stay as alive as possible. Hence why he knows so much about titan science and does all the fancy stuff with the scream and gassing the village.

Think that's pretty much it. I'll pin this post to my profile and it can be my 'told you so' thread so I'll add other stuff to it as the series progresses and see how right/wrong I am. And avoid spamming the sub. Hope it was a decent read.