More over none of them are bad or antagonistic for this, they are just human.
Now don't get me wrong, I like this manga a lot, and I do like that the characters have complexity and so forth. But, I often see people talking like realism consists in making all the characters neither good nor bad, and having anyone who
seems like an asshole turn out to just have stuff in their background that excuses it or whatever. And you know, that
isn't actually realistic. There are lots of actual assholes in the world, with no big things behind it except that's the kind of personality they have--or maybe, they were a bit spoiled or something, but other people with different starting personalities wouldn't have turned out like them with the same background. And contrariwise, I know a number of people personally who are pretty simply
good people--kind, generous, ethical, fairly altruistic.
Complexity and ambiguity can often make for a good story, and it does tend to
feel realistic, and quite a few people actually are complex and/or ambiguous. But many aren't, and not having any of those kinds may feel more realistic than it actually is.
Actually, one thing I like about this manga is that it actually isn't doing that. While some of the characters are complicated people, the interesting thing about the MC is that she mostly isn't--she's a cheerful, positive sort of person and with her, what you see is pretty much what you get, and if anything I think she's actively working to maintain that simple cheer in a relatively complex environment. She's not stupid, she recognizes that she could if she wasn't careful end up changing in ways she doesn't like, and she's decided not to.
