>>13515945>>13516012. That, and the way he looks makes more of a general "WUT" impression on me, rather than it being fear.
It's funny when you think about it. Stark *is* a Vasto Lorde. Chances are he's stronger than any Captain there except for Yama, even if he's just #3. Does he really have anything to be afraid of? Even Ulquiorra, who is below him, hardly ever showed any sign of fear. The way Aizen talked about the Top 3, at the very least, implied that just them along with their Fraccion is more than enough to steamrolle Gotei 13.