If there is a sequel to this, then it will probably started with Mafuyu getting raped again[or killed] while Nariyuki also getting raped from the girl, as the little sis say it outright that she killed Miharu off as she always get in the way. All of the girls except for Mafuyu and Miharu have all seen their happy end route in a form of a prophecy dreams, so they made the deal to share Nariyuki between themselves and Nariyuki doesn't know about it, anyone who broke the deal and try to take him for himself will be disposed even if they wasn't a part of the deal.