I realized that I've always focused excessively on Sora, the protagonist, when I was describing this game, so I thought (on a whim) that I would go ahead and introduce the heroines to you all.
1. Amatsu Kanata https://vndb.org/c8804
Amatsu Kanata is the first heroine in the recommended play order and perhaps the heroine who comes closest to Sora in personality. Selfish, cold-hearted, ruthless, and in possession of an iron will that would make a normal chuunige antagonist shudder, on the surface she plays the popular student council president. Her past is probably the nastiest and most victimized of the heroines, but the personality that past created is by several degrees the most naturally dangerous while being coldly rational in most ways.
Depending on which path you pursue for her, you get an ending where she takes the lead or Sora takes the lead. Ironically, she is far more forgiving and easygoing in the one where she takes the lead, and in the one where Sora takes the lead, her bloody-minded nature is far more in evidence, especially toward the end. Kirito (Sora's friend) describes her as being someone who, rather than taking a situation as it is and fitting herself in, molds the situation to her liking. He also remarks that taking such a course is the resort of a genius or a madman, while avoiding pointing out which she is.
2. Minami Mutsuki https://vndb.org/c4110
Minami Mutsuki is Sora's sex-friend, a whimsical senpai who has a tendency to play with words, deliberately poorly concealing what she wants in any given situation. Like Kanata, she is highly intelligent, but her personality is a great deal more mild and open. Part of this comes from the fact that she still has living family (a rather silly older brother and his wife), but a great deal of it comes from her essential nature. Sora remarks internally and to her several times in the story that she is a lot closer to being human than he is.
Unlike Kanata and Sora, Mutsuki is capable of feeling guilt, though only toward people she considers to be worthy on an instinctive level (a trait common to all the heroines is that they are unbelievably cold to people they don't consider equals under the surface). She is a hedonist, indulging in sex (with Sora), cigarettes, and frequent sleeping just because she feels like it. Outside of pleasure-related activities, she is mostly apathetic, but she has a sense of honor unique amongst the heroines.
3. Mukou Misora https://vndb.org/c4114
The only 'full adult' in the group. She is a teacher at the school and the older sister of Azumi, Sora's violently whimsical osananajimi. She is very good at hiding her desires and impulses, even going so far as to present a false face to Sora throughout much of her route. Unlike the other heroines, she has a strong desire to see Sora find some kind of normal, conventional happiness, though she herself is a bit too twisted inside to really understand such things.
Because she 'sees' too deeply, she misunderstands Sora's nature the most out of the heroines, save for perhaps Mei. Like all the heroines, she is coldly ruthless in going after what she wants, and she is also an inveterate liar. At the same time, despite her greater age, she is the most vulnerable (in every way) of the heroines, though her attitude toward people she doesn't like goes beyond cold into being outright murderous.
4. Nanagi Akane and Akari
Twin sisters who share all of their emotions and most of their sensations. Though Sora isn't aware of it, both of them have been in love with him since early childhood. Akane is the more rational of the two at the surface-level, whereas Akari is more primal and instinct-driven. As such, Akane has a tendency to fall behind Akari when it comes to acting on her emotions. In the setting of this game, twins who are also 'Enja', have to keep a careful balance between their wants, desires, and their fulfillment. If one wants to take one as a lover, one has to take the other as well, lest they gradually go insane.
Akane is very much a 'pretender', putting up a facade of geniality in normal life. However, she is also brutally sadistic and cold toward those she dislikes, while being somewhat cowardly and malleable in the hands of someone she loves. Like all the heroines, she possesses a strong urge toward violence and an inherently primal nature that goes beyond that of normal humanity. Other than Amatsu, she is probably the best at hiding it though.
Akari is kept confined to their home, due to the fact that her 'henshitsu' has already proceeded to a point where subtle signs of inhumanity have begun to show (eye color, a desire for the taste of blood, etc). She is not particularly dissatisfied with this arrangement, but she does wish she could see Sora. Unlike Akane, who is intensely jealous of her for something that happened in the past, Akari is deeply concerned for her sister. Also unlike Akane, Akari doesn't bother to hide her darkness, since she never goes out amongst 'normal humanity'.
5. Aono Mei https://vndb.org/c4113
To be honest, the best description of Mei would be 'innocent evil priestess'. Mei is like a more violent version of Hecate from Shakugan no Shana, as well as being even more innocent in some ways. Her only real interests are in her duty and in Sora... an interest that is profoundly unnatural given their natural positions within the natural order. While she is profoundly innocent in some ways, she reacts automatically to threats with excessive violence, often to the point of splattering those who threaten her without understanding they couldn't possibly know how stupid it is to provoke her.