Thinkin' bout the fact that the two kisses we've seen in the last few drhdr episodes mirror each other, on the way magic is used to either harm or heal. In fact I think they also may be the only two (focused on) kisses you actually see within the manga, which I find really interesting. One being Noi with Shin, to save Shin from being mushrooms, because she cares and loves him; the other with Kai and Natsuki, in which Kai uses it to distract and kill Natsuki via mushroom spores...
I think in the parallel between them it v clearly (as does the killing of Natsuki overall) contextualizes that Kai will not stop at anything for his goal, that he sees sorcerer lives as negligible... even those helping him, distinctly proving the point that Dokuga brings up on what Kai killing Risu demonstrated. In contrasting it directly to Noi and Shin, it's interesting because Noi has no scruples in killing people, and Shin basically as well... yet, they still care about each other and help each other, and (to a lesser degree) their friends/coworkers. With Kasukabe, it's clear that Shin doesn't kill him even though En would want him to and he's affiliated with Kaiman, because Kasukabe saved his life before, and he respects that, as does Noi. And Shin is even worried about Kasukabe when he wanders off! He cares, as does Noi, because Shin cares and Noi cares about those Shin cares about... But all of that is directly juxtaposed with Kai. This basic 'humanity' of care to those that help you is completely disregarded by Kai; in fact, there's almost something non-human (cough cough) about him, and the way he cold bloodedly pursues his goal.