It's rather interesting how Kana is genuinely evil. She comes up with malicious plots and has no inhibitions whatsoever about going forward with them. Normally people would hesitate or ask themselves if it's really okay and what might be the consequences afterwards, but Kana never shows any signs of such things. She of course values her home and her sisters, but I reckon she is a sociopath, and she only values them due to practical reasons and due to being used to them, as her life would obviously be hard and boring without them. In that sense Fujioka is quite a tragic character for having fallen for her. In light of this, I find harder to explain the rare signs of showing pity that Kana exhibit. I can't immediately remember other examples than giving Fujioka a bit of chocolate when she thought he received none. As a sociopath, she should be incapable of it.