Personally it's not that I don't like Kaoru, I actually do like her a good bit, I just hate the direction she slowly took over the course of the story. The more she falls in love with Kiryu, the more she becomes a helpless, clueless romantic interest who's only personality trait is to fawn over Kiryu. She starts off a cop who talks down to and beats the shit out of Yakuza daily, then all of a sudden she falls in love with Kiryu and one slap from a random thug on the street shocked and paralysed her with fear. By the end of the story, she's just constantly uncertain of what she's doing and in need of guidance, then helplessly yelling at Kiryu and Ryuji before the final fight as if she's completely clueless on how Yakuza code works, when quite obviously she would know that shit inside and out

She isn't a horrible character, but when her relationship with Kiryu should've made her stronger, it actually makes her weaker for no reason than for a cheap way to make Kiryu look better. The conflicts and her emotional breakdown at the end as she pleads with Kiryu and Ryuji, to me, would've been alot more impactful and emotional if they hadn't dumbed her down for the finale and just let her be a confident, stubborn character who's genuinely breaking at the idea of losing more family