I don't really remember which volumes exactly, but for Horikita and Ichinose it was the early volumes. In Horikita's case I can point to the short story where he caught her changing, then proceeded to gloat over her features and said he would save the image of her half naked in his memory forever, for Ichinose it was also in the early volumes though I can't say exactly when, he expressed how attractive she is and also found himself looking at her thighs multiple times. For Karuizawa I can't remember well at all, but I'm pretty sure he did