Ken is entirely startled by the kiss - the number of times Chikusa has initiated affection between them, even after all these years, probably numbers less than a dozen - but the way he beams as it sinks in afterwards more than makes up for any delay in positive feedback.

And then, because self-control isn't a thing Ken possesses, he's all but lunging at Chikusa, pressing him against the wall and nipping roughly at his throat in sheer exuberance. But it's only a moment before he tears himself away, too soon for even Chikusa to complain, popping his Cheetah Channel cartridge into his mouth before bolting off. The fact that he actually left rather than pursue things further is, oddly, a sign of obedience; he's sticking to Chikusa's plan, even as excited as Chikusa's spontaneous show of affection has clearly made him.

Chikusa can only pray he hasn't worked Ken up with that to the point where a peaceful blowjob won't be enough.