Gotta say, love when Kaoru comes up one way or another because people will break into "hate her" vs "kinda like her" warring camps.
Anyhow, thought I would throw two cents in: I actually think that what Mask did was worse. Like, don't get me wrong, Kaoru is a cunt and a bad person but she always came off as a himbo to me: overly confident, horny, and stupid. Stuff that she did, she did not out of cruelty or whatever, but because she simply did not think. Mask's feelings, however, are very much cruel. And also yes, might as well go there, I also thought that Shizuka was worse than Kaoru.
Remind me if I am wrong, but wasn't the shtick that Mask would go for Kaoru because she wanted to "experience new stuff" to be better at drawing? Or something like that: with Mask viewing herself "as bad of a person as Kaoru", and thus seeing Kaoru as the only person who would get her, we could go do that route sooner than later.
I, honestly, wouldn't mind seeing more Kaoru. I wonder if the manga will go for "she became a better person" bit or for "she is a himbo who can exist only in an open relationship" bit. Either way, ass or not, still the second prettiest character in the manga (I swear man, those genes.)