This is ridiculous. MC needs to straight up confront that class, and ask why they're immediately willing to lie about him on the whim of one person acting like a POS, then treat HIM like the villain somehow. I get the bully trope, but usually most of the class are passive with a few enjoying the show, and a few bothered, but afraid to speak out. But in this the whole class are villains actively being hostile, and even all of them refusing to help the wounded in the castle.