Shu is always in trouble with money but manages to live thanks to the support given by his ex-girlfriend Ayano and the ever-devoted Kisara. The same goes for his job as a PMC. With Ayano's cooperation, Shu won a bidding war at a discounted price to participate in the "D Hazard" prevention operation that occurred in a casino. At the scene of the demon extermination, he planned to rely on Kisara's demonic powers, but she is nowhere to be found due to the money situation ruining her mood. As a last resort, he works with Ayano's leading, major PMC and confronts the Demon, but bit by bit, the battle becomes something suspicious...

Kisara is in a great mood after getting a duplicate key to Shu's apartment. On the other hand, Shu can't find any peace of mind when she gets ahold of the company's financial situation without permission and increasingly encroaches on his daily life by pretending to be his hidden mistress. But even more problematic is the current lack of living expenses. Shu finds out that the incoming deposit he was relying on is still on its way due to a misunderstanding, so he asks Ayano for some contract work. And thus, Shu and Kisara find themselves safeguarding the 25th anniversary party of Bayron City and protecting the mayor from terrorist threats.

A large-scale power outage hits the heart of Bayron City's Downtown. It was a D Hazard caused by a giant caterpillar-shaped Demonically Possessed. With detailed information on Demon Possession that he obtained from somewhere, Shu decides that this is a job that "must be done" and uses Ayano for insider info to pull strings. As Shu's company is about to win the bidding war at a discount, significant new information about the Demonically Possessed is revealed. Those who took the situation most seriously decided to suspend bidding and expelled Shu from hazard prevention measures.

Although the Demon Possession that caused the large-scale power outage was exterminated, the problem remains unresolved as the power shortage in Bayron City continues. Meanwhile, Kisara witnesses a secret meeting between Ayano and a mysterious man. To confirm Shu's feelings, she uploads a photo of the scene to social media. Successfully lured by Kisara, Shu rushes Ayano and the mysterious man – an Anti-Demon Bureau detective named Tetsuya Mikami – and, in an unexpected flow of events, realizes that Ayano was hiding her intentions and planning behind his back. An unparalleled sense of tension lofted between the two.

Ayano has become a target for Demon Possession. Although Ayano narrowly escapes her first attack with Kisara's help, she begins a life of isolation to hide her Demonically Possessed eyes. Meanwhile, Shu is offered a chance to work together by Mikami, who is familiar with Shu's past. On board with the discussion, Shu discloses information to Mikami and his team at the Anti-Demon Bureau. They are trying to determine the identity of a Demon Agent producing Demon Possessions one after another. They step into a certain dwelling, but...

Kisara keeps her distance from Shu's apartment since she saw the memories of Shu and Ayano's time in the warehouse. Reversely, happy for Kisara's absence, Ayano takes good care of Shu as she relishes feeling like they are lovers. Kisara, who checks out the situation via social media, is getting increasingly more annoyed. But behind the scenes of this love triangle is a storm of violence that blows into Bayron City. Just who is this blonde beauty who appears out of nowhere wearing a nun's habit? And what is her goal as she repeatedly commits senseless acts of brutality by invading scene after scene of Demon Hazards?

Thanks to Shu and Kisara's efforts, the Anti-Demon Bureau successfully detained Sharon, and peace returned anew to Bayron City. With his companions Mikami and Miles, Shu once again pursues the truth behind the continuous D Hazards that have been manipulated by some entity's volition. They continue compiling deductions to pin down the identity of the "True Agent," who they presume is lurking behind Junya Hanamura, the murdered Demon Agent. At the pinnacle of their deductions, Mikami reaches a certain conclusion and tries to contact Shu in a hurry...

In the chaotic mix of humans and demons, Shu and Kanna meet in a violent clash worthy of their 12-year-gap as various motives intermingle in a battle engulfed by a sea of flames. Ayano, Sharon and Kisara try to somehow intervene in the siblings' fight that puts the fate of the world at stake. The only way to stop a powerful demon is with the power of a demon. Shu and Kisara join hands once again. Will the accumulation of their feelings reach Kanna, embroiled in her rage? At the end of the battle, what future lies ahead for humans and demons alike?