Strange occurrences at sea result in Itogami Island becoming isolated. Nagisa continues to suffer effects from her previous exertions. A terrorist group known as Tartarus Lapse begins operations on the island.

The terrorists launch an attack upon the warehouse district. Afterward, Kojo and Himeragi meet the terrorist leader, Senga Takehito, who tries to recruit them. He reveals his beliefs about the true nature of the island, its purpose of reviving Cain, and his plans to oppose this.

At Mogwai’s urging and with Motoki’s assistance, Asagi makes her way to the Keystone Gate in order to end the hacking attack upon the island’s network. Meanwhile, Kojo and Himeragi battle ineffectively against the demons unleashed by the terrorists.

Kojo and the others go to rescue Asagi, who was imprisoned on the 0th floor of the Keystone Gate. Kojo is worried about Himeragi's poor condition, but Himeragi goes with Kojo nonetheless. What was waiting for Kojo and Himeragi on the 0th floor?

Kojo and the others are helpless by the power of Meiga Itogami's Cleansing ability. Kojo wonders what the hell this Cleansing ability is. At that time, the truth about the Cleansing is passed on to Kojo. Will Kojo be able to protect Himeragi and Itogami Island from Meigawa Itogami?!

Itogami Island had returned to a peaceful state and Kojo's party was getting excited about the upcoming Valentine's Day. Meanwhile, Kojo sees Asagi getting into a car with one of Vatler's subordinates, and starts to get suspicious. Grenda, who was with Shio and Yuiri, is attacked by Veres Aladar, the Imperial Council Chairman of the Warlord's Empire. Grenda flees to Itogami Island, where Kojo is located.

Kojo goes to Iblisveil Aziz in search of answers on how to defeat Veres Aladar, but Iblisveil only gives Kojo a vague answer. Kojo returns to the agreed place of the duel shorthanded and begins the duel.

Kojo wakes up at Natsuki Minamiya's house. On TV, Asagi and Vatler appear to be working together and declares war against the Holy Ground Treaty Organization. In addition, Asagi says that Grenda will use Cain's legacy that she has protected as her power, to help save Itogami Island. Meanwhile, to save Nagisa, whose life is in danger, Hektos tells Kojo and the others that she will need to hold a ceremony.

With the help of La Foria and Veres Aladar, Kojo broke into the council and declared Itogami Island as his territory as the 4th Primogenitor and gained the right to veto the attack. But for him to be recognized for this, he must expel Vatler from the island and become a true ruler. Can Kojo defeat Vatler, who has absorbed the power of the Cleansing, and save Itogami Island from the crisis?!