Shock
Surprise
Bewilderment
Imagine all the words that can used synonymously for surprise and you will see the expression of all the second graders. Only a few people are not really surprised. Because ever since this Set academy guy started fighting, people are wondering how they can counter that.
Not just the second grade people, even some third grade and some rare fourth grades are also wondering how to counter him. Because a lot of them didn't even understand the ability. Some did understand it, but couldn't figure out a counter.
Rashma who usually acts like a barbaric brute has figured it out a lot faster than most people.
That confident kick is the direct representation of her understanding.
As for what the ability is…
The other guy also has a rare constitution. His body can turned into a specter at his will. In a way it is kind of a fusion form with soul energy.