Air and sea transportation to Itogami Islandhave been cut off entirely.Meanwhile, key personnel of the Gigafloat ManagementCorporation are being assassinated one after another.The mastermind behind thisseries of incidents is the self-proclaimed Demon Sanctuary Destruction group,Tartarus Lapus.Nagisa is still suffering spiritual fatigue due to the awakeningof the soul of Avrora.At this time, she meets a strange girl who goes by thename December.Unbeknownst to Nagisa, this girl is the leader of Tartarus Lapus,and she has a special ability capable of overwhelming even the FourthPrimogenitor!