Kareha Banouin led the Dominion's forces in the war against Hod's rebels, and she's the one who made sure the whole conflict stayed non-lethal. Fans often note that her real motivation was simpler than her official role suggested—she mainly wanted an excuse to fight Retsumi Jugasaki, the opposing general, because she enjoyed their rivalry.
In public, Kareha played up a refined Japanese princess persona, complete with a fake Kansai accent that she'd occasionally slip out of. Behind that polished act, though, she had a mischievous, devil-may-care personality much like Kurumi's. In a normal school environment, she'd probably be the type to keep to herself, without a real friend group.
The confidence was a front. Underneath, Kareha was dealing with something darker—her heart was being corrupted by love for the White Queen, and she was slowly transforming into an Empty. Once she realized what was happening, she started avoiding Mizuha altogether. It's telling that she never actually confronted what was going on with her feelings.
What she did do was trap Hod in eternal summer, ensuring that her endless game with Retsumi would never have to stop.
Content compiled by AnimeList.moe from publicly available sources.