He just goes with it.

Seeing that Satsuki was probably not in the mood for a rational discussion, that left Kazuma with three options: escape, fight her, or go along with her. He didn't think he could escape her. She was faster than he was, and with the door closed, it would take a bit to get out of the room. He didn't want to fight her for two reasons. The first was that he didn't want to hurt her. The second was that if he did start a fight with her, it would probably not look good to anyone coming in and checking on the commotion. They might think he started the fight to **** her, and that would not end well.

Give that, Kazuma decided to stay and go along with whatever she was planning. His hormones were also a deciding factor, as it seemed like she wanted to have sex. But before he does anything, he should find out what she wants.

"What are you trying to do and why are you taking your top off?" Kazuma ask.

"It's pretty obvious," Satsuki answered. "We're having sex!"

Kazuma was surprised that she was so blunt.