YES!!!! I'm loving yandere Yuka. My ideal ending is now everyone but Kakeru dying after Yuka merges with the demon loli and all the other fragments. Then Kakeru has to banish the demon lolis soul to hell with his magic eye but sacrifices his life in the process (I kind of hate when heroes survive crazy super magic that should involve some sort of heavy penalty with no ill effects). The final scene would be an un-yandered Yuka on the roof of that giant building in the real world cradling Kakeru's lifeless body and screaming bloody murder at the heavens. In this scenario Kakeru can still have sex with Kusakabe after Yuka gets absorbed but before she manages to kill everyone else. I would buy Kakeru being vulnerable and in need of comfort after Yuka's absorption and his and Kusakabe's narrow escape from the Red Night after witnessing Index girl and maybe the knights getting slaughtered by Liselotte.

But of course that's never going to happen so I'd rather see Kakeru get with the girl I feel like he has stronger romantic feelings for (Yuka) then see him put with the girl I'd prefer to get a happy ending (Kusakabe). I definitely think Kusakabe has earned something good happening to her but I wouldn't like seeing Kakeru turning his back on his relationship and feelings for Yuka to accomplish this as it would feel odd. That said, Yuka could still die as part of Lislotte-Yuka whic would facilitate a Kusakabe x Kakeru ending after an appropriate amount of emotional healing time for Kakeru.