Ein Riese, der Fliegen Wollte (слэш)

He needn't have worried. The small one was strong.
He sees the human many more times since then. It seems as if the herd doesn't venture out without it. He wonders if that one is the pack-leader. It seems logical, but humans are not always creatures of logic.
He forces back memories of that one, and continues to shadow the herd whenever it ventures out. He makes a habit of waiting in the small grouping of trees near the gate so as not to miss one of their outings. Eventually he learns to distinguish the small one from the others even before it takes to the air, and he feels proud of this accomplishment.
Months later, only hours after the humans had returned behind their walls, everything changes.
(In which Eren is not a human that can turn into a Titan, but a Titan that can turn into a human.)