Magical Girl Raising Project, Vol. 15 (light novel)

Although they've come up with stopgap measures to restore their powers, the great mage Sataborn's heirs and their magical-girl companions are now scattered across the island that is holding them captive. To escape, they must defeat the tyrannical goddess who has been slowly killing them off one by one. The survivors continue putting up a fight despite their struggles...but who is controlling this goddess, and for what purpose? Is the real enemy hiding in plain sight...?