Here's the endgame. (spoilers for eternal champion and dune series)

SNK is based in the book "The Eternal Champion", and the characters seem to have references to characters in the book this way:

Erekose (Protagonist) = Eren (They both swore to "kill them all", and they are destined for tragedy by forces beyond their understanding)

Iolinda (Human princess) = Mikasa (They are both very jealous and both accuse the protagonist of sympathizing with the enemy, remember Annie)

Ermizhad (Eldren princess... yeah her race is called Eldren and The Eternal Lover) = Historia (They are both blondes and have blue eyes, both had a sibling who had the key to unlock the ancient power of the Eldren people, remember Frieda)

https://en.wikipedia.org/wiki/Eternal_Champion

Erekose reincarnates to be the savior of mankind and has dreams in which he can see his past and future lives (as the user of the coordinate can see his previous and future users). In addition he is stuck in a battle between two sides, humanity and the "Eldren" The Eldren have an old power that almost destroyed the world and its ruler has decided do not to use it even if that means the extinction of its species -the 145th king-)

He is destined to commit genocide of some kind, and at some point says "I swear I would kill them all"

His ultimate end is suffering and inevitable demise.

Erekose sounds like Eren. Erekose marries Ermizhad an Eldren princess who is described as a blond woman with blue eyes.(gewijzigd) Eternal Champion

Yeah, SnK is based on the Eternal Champion, but it's also based on the Dune series.

Shifter memories are kind of like the Spice. It expands consciousness and allows some access to past memories via genetics.

The Coordinate power seems like when Bene Gesserit ingest huge quantities of Spice and get full access over those past memories.

Those who inherit the Shingeki no Kyojin are akin to Kwisatz Haderachs. They have access to past memories, but they also gain prescience.

Some SnK shifters like Grisha see the path they must take to deliver man into true freedom but reject it because they must take drastic actions they don't agree with.

Eren Yaeger and Leto II see the Golden Path and reject their humanity in order to enact their visions. Many think of them both as tyrants but they're helping humanity through their actions.

I think in the end, Eren will become the God of mankind. Only the closest to him will understand his actions and possibly only at the very end of the story. I think someone is take the SnK powers from him, but his plan will already be enacted and won't be stopped. found something else on eternal chapion Titan thunder during transformation The thunder is a reference to "Stormbringer" the most famous version of the "Black Sword". A weapon that can devour the soul or life of it's owner in change for a great power. This "black sword" is an element very important in the books about the Eternal Champion, the principal influence behind Shingeki No Kyojin. Here you can see an analisis about the Ymir and the Titan and how it's vinculated to the Eternal champion and the Black Sword I think that all this thing about a deal between a devil and a girl is more a subtile reference to the Eternal Champion (Book that seems to be the biggest inspiration for Shingeki No Kyojin) and it's relationship with the Black sword than a metaphor about Historia and Ymir. Making long story short... It's a pact between the ultimate good (The eternal champion) and the ultimate evil (The black sword) that make of them a figure that bring balance to the world. With this pact the champion bring peace or destruction, he is the savior or the destroyer. (you can see a refence to this concept in the song Bauklotze for the anime) Ymir Fritz is the "Eternal Champion" and the Titan is the "black sword" the hero weapon with the which Ymir Fritz made a deal... in the same way the 145th King made a deal with this Titan. https://en.wikipedia.org/wiki/The_Eternal_Champion_(novel) PD: The sword is evil and it eat the champion soul and this make the life of the various champions very short. (Like the Titan Power)

Will history repeats itself - how Girisha helplessly watch Dina being turned into a mindless titan right in front of his eyes? You know I have been thinking in this and... after of compare it with the original work in which Shingeki is inspired I have to say that... I don't know... Althought It's likely (and I don't like it...) and It would be good if you try no analise It too. In The Eternal Champion the hero in all his lives always have a romance with a woman and she is called "The Eternal Lover" and she reincarnate with the hero. Eren and his past lives The Eternal Lover = Dina and Ermyzhad [Eldren/Eldian Princess in the book (Historia in SNK, her similar look with Dina is a reference to the Eternal Lover and her reincarnation cycle just like Eren/Grisha/Kruger)] talking about Ermyzhad... it seems like she is a blonde girl with blue eyes. Ermizhad The problem with this Eternal Lover is that... um... she is a tragic figure and the hero (Shingeki No Kyojin vessel) is always unable to protect her from her enemies or stay with her for the rest of his short life (because they are separated for the destiny). Soo... I don't really know what will be Historia's fate... It's possible that Eren break the destiny (how it is a regular topic in SNK) or he fails like Ymir did or Uri and others characters who fail in break it. PD: I have the feeling that Isayama tried to represent Ermyzhad with his character Annie since she is blonde and has blue eyes too (and she belong to the enemy nation) and Mikasa hate her just like Lolinda Princess hated Ermyzhad... but in some point Isayama discarded this idea for unknown reasons and he moves up to give this role to Historia.