I highly doubt she would be offended by people not liking her music. It's just what all artists have to deal with during their entire career. FIVE isn't the first album of all time where someone doesn't like it lol
But at the same time, if people literally tweet her saying rude things or saying how they don't like it, that's just uncalled for and they should get a life and leave her alone. She doesn't need people being negative directly to her. Whine all you want about how much you don't like it on places like a forum, but saying it to ayu herself is just... not needed
And also if she's feeling down, I'm sure she'll talk about it when / if she wants to. We can't expect her to reveal every detail of her emotional life to us
