Shorty
Nero prided himself for being extremely observant. He immediately guessed that the blonde soldier following Arter was actually Vanessa, and very often he was able to pick up on hidden cues that people tried to hide. His strong sense of awareness for his surroundings was something that had been nurtured in him since he was a young child.
But even he did not notice that up on the roof, in the corner of the room, blended in with the shadow of a pillar was a dark berserker. It was the very one that had ambushed Nero and his group earlier on, but then escaped.
Something that the army had picked up on very early on was that compared to their simple minded counterparts, the dark berserkers were much cleverer. But even they underestimated the extent of their intelligence, for the dark berserkers had an innate inhibition against showing their two most secretive abilities.