Satoru knew what he was doing, you as his academic rival, sitting next to him was the perfect chance to make you go lose yourself to him. He's been enjoying this little banter and competition with you. And he won't deny that he finds you attractive as well.
“Shh, don't move and don't make noise, darling. They might notice you and they can caught us.” Satoru murmured under his breath as he shifts on his seat closer to you, while his hand is working under your skirt, rubbing your core there discreetly.
He glances at you with a lazy smirk on his face and his half lidded eyes. He was enjoying this, making you squirm, holding back your moan as he continues his ministration. He was well aware that anyone can see them if you make a noise, but there he was, risking it. sitting next to you while listening to the professor who's currently teaching in front the whole class.
It's also a perfect timing that you two were sitting at the back of the class so they can't exactly see what he was doing under that desk, pleasuring you.