Humanity's Wings (riren/ereri)

Then end was coming Eren Yeager knew this as he watched Levi Ackerman fly towards him with his blades at the ready. He didn't fight as the Captain approached getting closer and closer as those blades cut his nape. His freedom was coming. The only freedom he deserves after what he'd done. He felt as Levi hesitated before finishing him off. As he severed head fell toward the floor the sound of rain became muffled. He'd done it. His people where free but at a cost that was large. Oh how he wished things turned out differently.

He regretted how things turned out and wished things went differently.

A boy in a shelter with a key around his neck Shot awake gasping for breath.

Or Eren Yeager time travels.