Grace's goal isn't simply destroying the Vajra, that much is certain. Whatever her grand scheme is though, it certainly seems to include sacrificing them as part of the means to reaching that goal. As much could be deduced from last episode's dialouge. Since Grace seems to need Ranka as well to carry out her plan, The Quarter (
) seems like the most likely candidate to foul up her plans. Leon's hope of fouling it up seems be by manipulating Alto into killing Ranka.