In a post-apocalyptic world overrun by vampires and demons, humanity survives behind the protection of the Japanese Imperial Demon Army while elite squads fight across the ruins of destroyed cities. You join a newly assembled squad alongside Yuichiro Hyakuya, Shinoa Hiragi, and Mitsuba Sangu after being labeled a mysterious “irregular asset” tied to classified Seraph experiments. As vampire attacks grow more violent and entire patrols vanish without explanation, the squad is sent deep into abandoned cities, underground strongholds, and forbidden military zones to uncover the truth. But the deeper they go, the clearer it becomes that the war between humans and vampires hides something far older and far more dangerous. Ancient powers tied to the apocalypse are awakening, demons whisper through cursed weapons, and dark secrets buried by both humanity and vampires threaten to ignite another catastrophe. Caught between survival, loyalty, and the horrors lurking beneath the ruined world, your squad must decide who can truly be trusted before everything collapses again.