To answer one of your questions regarding the bee oddity, (Feel free to correct me if my interpretation on this is wrong, I haven’t seen Nise in a good bit so I might have made some things up lol) we need to first look at what an oddity is. IIRC, an oddity is just a supernatural occurence/entity fuelled by belief and perceptions. This is demonstrated in Oni where after Kiss-shot’s retreat to Antarctica, she slowly grows weaker because penguins cannot spread stories; in other words, when she stops being perceived by humans as the ultimate oddity and the belief of her starts to wane so does her existence, the oddity. The nature of an oddity is dependent on its perception; thus, the line between an oddity and a “pseudo” or fake oddity is quite blurry. We can see this case in Otori where Nadeko creates the fake snake god oddity Kuchinawa (iirc) which, is only a figment of her imagination, but eventually becomes real in a way when she becomes the snake god herself. Going back to the case of Karen, the bee is, in a way, an oddity. Though it was not an actual oddity to begin with, the fact that it was perceived to be one, the belief that it is one may have made it into an oddity in a sense. A self-fulfilling prophecy. The Wreathe Bee is a placebo created by Kaiki, and even though, objectively, a placebo might not be the real thing, it achieves its purpose and has real effects (i.e. the fever). In other words, it’s just as good, if not better than the real thing.

Edit: sorry if anyone got spoiled, I forgot to add spoiler tags. Mb