It's from Mikuni, pee girl, after he broke up with the teacher. She's talking to him in an empty classroom when they hear someone coming so she hides under the teacher's podium and he stands behind it. The person coming was the teacher, his ex, and he starts having lewd thoughts about her, which crotch height Mikuni sees the results of and gets jealous, so she decides to go to town. It's something straight out of a porno with him trying to keep his cool until it shows the teacher's thoughts that not only is she making a LOT of noise, the podium doesn't have a bottom to it in the front so she can clearly see Mikuni is down there. It starts at Ch. 123 and goes throughout 124.