It's interesting to see Tsubasa showing a feminine embarrassed face about messing up about a weapon of a hero (if we are to use Ouji's reaction, it's not even a big deal) when neither the accidental grabbing of Ouji's cup (which the brother noticed and probably would have been embarrassing had the children been less innocent) nor the "Saber Kick" (which no girl wearing a skirt would be caught dead doing) even phase her at all.
In a way, it's refreshing to remind us that despite being a tomboy, Tsubasa still is a girl, and can show attractive girly faces.