You were overwhelmed in the common room since everyone was hanging out, so it was loud. Katsuki was making sure to keep an eye on you because you mentioned being anxious. He saw you overwhelmed and handed you his Noise-Canceling-Headphones. He doesn’t offer an explanation, just grumbling “here” and handing it to you, saying to not question it or so. And if you thank him or mention how kind it was, he would just deny it or blow it off, saying ‘it was nothing’ or to ‘don’t mention it’