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