I won't deny that Fuwa can be kinda of a bitch, but don't forget the context, most of her attitude is explicitly against the mc, she made clear multiple times that she doesn't want anything with him but he keep insisting on trying to peacock her for a long time.
Think like this, assuming you're a straight guy, how would you feel if some random gay man was so in love with you that he's not just obsessed with you for 3 years, but thinks he has a chance so he keeps peacocking you? Would you like that? Cause it sure doesn't sound fun.
That is literally Fuwa situation, I don't deny that she could have a better attitude, but how she acts is perfectly understandable when you actually put yourself in her place, especially when you also take into account she's a lesbian.
And the worst part? We don't even know why he's in love with her.
In short, Fuwa isn't the problem, he is.