This is just my personal take on why I gravitate towards this character but, I think I like Chinatsu from this series for the same reason that I like Kurusu Hiro from "Kono Oto Tomare", in that their initial introduction as an inherently unlikable and antagonistic individual, as long as they are SOMEWHERE on that scale even if they aren't actual antagonists, comes into a direct clash with the actual relationships they end up forming once they get over their own individual hangups. Case in point, Kurusu comes into Kono Oto as someone trying to break up their club, proceeds to rub everyone the wrong way and eventually enrage the club's president and greatest pacifist, Takezou, who continues to hold a... questionable opinion of her personality for the rest of the series. Given that he's the person who assists her recovery from her depression and insecurity, and stands up for her the most, she develops a very strong crush on him which she herself struggles with after her intentional efforts to destroy his club. It's this very conflict that I appreciate the most. Male or female, if a character is introduced in a way that is might disgust the audience, then grows outside the confines of their original character constraints and then begins to hate those parts of themselves by which they were originally defined, and desperately seek to reach the kind of purity they assume the original cast has, I find that to be powerful. Koe no Katachi gave me this feeling in the utmost, more so than pretty much any other series I can think of at the moment, where watching that boy awaken to his hideous actions was like watching a demon in the pits of hell scream out for God. In Hiro's case, she wasn't nearly as horrible as that boy from Koe no Katachi was to that deaf girl, but she is spends a good minute screaming at herself for loving someone who "deserves better than her". Chinatsu is a bit different from these cases in that she doesn't quite thinks of herself as behaving terribly towards Tatara in the beginning but rather just views her personality when juxtaposed with Tatara's endless font of forgiveness as an impossible scenario, then beats herself up (ala the scene where she's crying uncontrollably into her bed after berating Tatara) while unavoidably still being the mean kid that she is. Yet that conflict between wanting to be his partner, and yet treating him horribly, then fearing that her treatment is destroying what she wants, it all still exists.
Anyway I've rambled on enough, tl;dr - I'm a sadist who likes to watch shitty people suffer the fate of growing enough empathy to be pained horribly by who they are, because imperfect people are far more beautiful than perfect ones to me.
Doubt any of this is of help to anyone, it's just my weird-ass opinion, but this thread is empty and I figured I'd contribute what little I've got.