Something to remember...

"What...?" Eren was completely thrown off at this point. If he remembered correctly, the titles he held were: "The One Who Shouldn't Have Been Born," "The Catalyst," "The WILL's Greatest Foe," "The one who couldn't die," "The Fallen Hero," and... "The Doorway to the END." 

But... if he was the supposed Doorway, and this entity was the alleged END, didn't that mean his sudden growth in power was connected to this very entity?

"What do you mean by... the one and true END...?" Eren asked, halting his step and standing still, waiting ever so patiently for the voice to reply.

"...I don't know," came the reply, blunt and uncaring—something even Eren could see through. It seemed this entity wasn't exactly... an ally.

"I can hear that..." added the enigmatic voice, and Eren clicked his tongue, realizing how disadvantaged he was against this... THING he couldn't even see.

"Alright, you win," Eren said, though it was only meant to throw the creature off as he began thinking while talking. This way, the entity shouldn't be able to hear his thoughts... he hoped.

'There wasn't any mention of this in the game, or is this perhaps one of the mysteries I never got to uncover since I didn't play till the end...? Tch... Talk about a dilemma. If this guy was really the one who Eren me into the villain he was, then he's bad news. But... I can't do anything about it since he's now attached to me. Perhaps he really is related to Eren's bloodline heritage,' Eren thought before taking a step forward once more.

He had to find at least some shelter before night came, or things would really get out of hand.

In the game, just before the academy arc, there was a mention of a group or an alliance of sorts... Opposers of the Old Religion, or something along those lines.

Eren didn't really understand their true objective, but it seemed they were trying to revive the demons. Or... that was what he had concluded they were after, since their true objective was always shrouded in mystery. 

But... it seemed they were after something called...

"Hm...?" he blurted, drawing even the enigmatic entity in his mind to pay attention.

"What's wrong...? Done rambling that nonsense?" the voice asked, and Eren realized the voice could actually hear his inner thoughts, no matter how much he tried to mislead it.

"Listen here, we are stuck together whether you like it or not, so it would be better if we work together. I help you, and you help me," the voice offered.

But Eren gave no reply. Not because he didn't agree to the offer, no...

Instead...

'Why...? Why do I feel like I'm forgetting something important?' he frowned as his brain kept trying to figure out what exactly he was forgetting. He was sure of it...

He was sure... it had something to do with...

The MAD GOD.