This questions needs to be asked regardless of whether the story is a Harem or not because even in Harems there is one girl that the Main character prefers over all the others like Rias was for Isse in High School Dxd, and she is the one that controls the Harem.
I want to know who is the Alpha Female of the story that one that controls the others because there has to be someone that he loves above all others.
I especially want to know if the person that he loves the most is his sister in the story because she has the highest affection value of any of the others.
Nor do they fight over Kazuki since they know that he becomes stronger with more girls (variety of magic) and the stronger the relationship with each girl (power and choice of spells). Interestingly, allies can be included in the available magic even when they are not fighting together with Kazuki.
This is one of those few light novels where every girl in Kazuki's harem gets their time in the limelight. They don't get jealous' when Kazuki is spending time with another girl. Hell, the girl who everyone originally pegged as the tsundere was initially upset (with good reason) because Kazuki forgot who she was. When he remembered and actively made an effort to get closer to her, Mio switched from TsunTsun to Dere Dere (passive agressive to very affectionate) with very few cliché passive agressive moments.
Best example: Kazuki took Hikaru out on a date and ran into Mio at a clothing store. Rather than get jealous, she simply tells him to keep her in his heart and to not neglect her (which he does. As in goes spends time with Mio). Kazuki has no favorites among the girls. There's simply the magic compatipility points between them. He loves them, they love him. No competition for who get sto spend time with him or any other harem anime cliché shenanigans.