Probably the only reason Ken doesn't put up more of a fight is because he genuinely doesn't think anything's wrong with it; if he thought there was a chance he might have to get some kind of medical attention, Chikusa would probably have to chase him down. As it is, though, Ken just makes an annoyed sound and lifts his hands briefly, looking away.

It still looks like his dick, certainly. It also looks like he's lost interest in the proceedings entirely.