A storm had come to Brockton Bay, and with it the sound of Sirens. Leviathan had come, very much ahead of schedule, and without warning of any sort. But that wasn't the only odd thing that the responders found. For the Endbringer was not attacking, nor was it really moving at all.
It simply sat in the center of the Bay, flicking it's tail back and forth. It was here that the first truly clear pictures of the beast were taken, courtesy of the Tinker Viewfinder, who sent his camera drones as close as one meter from Leviathan's body, taking images from all angles.

After the first two hours, tension started to both grow and rise. While on one hand Leviathan wasn't trying to kill anyone or destroy the city, this behavior was completely unprecedented. Eventually it got to a point where some of the gathered Parahumans grew restless enough that Leviathan's first major movement, tilting it's head about twenty degrees to the left, caused Megaton, a high-level Blaster from San Diego, to fire on it with one of his replicating plasma charges.
The resulting twelve projectiles garnered no movement from the Endbringer whatsoever.

The next change occurred four hours later, when Leviathan extended it's right arm to a fully horizontal position, while it's left arm went straight up in the air. It maintained this position for exactly forty-five seconds(measured to near-exaction after the event by Dragon), before swapping the pose to the opposite sides.
Once again, it came under attack, this time from Bakuda, whose drone-delivered explosive charge reduced it's right arm to glass. Again, there was no counterattack.

Three minutes later, an unearthly sound reminiscent of whale song echoed around the foggy expanse, to which Leviathan responded in kind. After that, it spent only one more minute outside the City before retreating back into ocean, leaving the glassed arm behind.
Afterwards, the two recorded sounds stumped experts as to their purpose. Some postulated that it was nothing, just an intimidation tactic and that the whole event was made to mess with them, while others theorized that it was a mating cry, based on the similarities of the sounds.
That raised more than a few eyebrows, and many more alarms.

Still, at the moment the phenomena had no explanation. This would soon change.