Setting The game takes place in
near-future Tokyo, and follows detective Kaname Date of the top-secret police department ABIS (Advanced Brain Investigation Squad). ABIS, led by Boss, investigates crimes through a method called "Psyncing", in which Psyncers explore the dreams (known as Somnium) of subjects via the Psync Machine. Psyncing is a process that can retrieve clues the subject is subconsciously aware of, but is limited to a maximum of six minutes for the Psyncer and subject's safety. Any longer than six minutes can damage the brain of both the Psyncer and subject, resulting in death. Date is assisted by an artificial intelligence housed in his
cybernetic left eye named Aiba, who can communicate with Date, provide him with enhanced vision modes, and hack various electronics. Aiba also assists Date's dream world investigations by acting as his avatar in Somnium. Date, who lost his left eye and all his memories six years prior, is called to investigate the murder of Shoko Nadami. He finds her daughter Mizuki Okiura at the scene,
unable to speak. Date investigates Mizuki's Somnium to find out what she witnessed. Throughout his investigation, he meets several others at the center of Shoko's murder: Renju Okiura, Mizuki's father and Shoko's ex-husband; Iris Sagan, a
net idol employed at Renju's talent agency; Ota Matsushita, a fan of Iris; So Sejima, a member of the
National Diet; Hitomi Sagan, Iris's mother; and #89, an imprisoned assassin also known as Falco. The plot is structured in five routes based on the player's choices in the Somnium: the left branch, which is centered on a series of murders called the New Cyclops Serial Killings, consists of the Ota route, Mizuki route, and Annihilation route; and the right branch, which discusses Date's past and the events of six years ago, consists of the Iris route and the Resolution route. The Annihilation and Resolution routes are not fully accessible until the player gathers information from other routes.
Plot Left side In the left branch, Date initially claims evidence that Renju may be behind Shoko's murder but later finds him dead on day 2 with his eye also missing. Boss believes their deaths are part of a new string of serial murders reenacting the Original Cyclops Serial Killings from six years ago due to their right eyes missing from their corpses. On day 3, Date Psyncs with Iris due to being seen with Renju a few hours before his death. After Iris is released from questioning, she flees with Ota's help, but she is later seen about to be murdered in a
live streamed video. Date suspects that Sejima is the New Cyclops Serial Killer due to his connections to Shoko and Renju through the . In the Ota and Mizuki routes, Date prevents Iris and Ota's murders, but the mystery is never fully solved. In the Ota route, Ota becomes concerned when Mayumi, his dementia-ridden mother, is named a suspect. Mayumi is proven innocent, but Sejima's dead body is found. Date is still at loss as to who the murderer is, as new evidence implicates Iris as the murderer. In the Mizuki route, Date secures DNA evidence that Sejima is the murderer, but Sejima, who has power over the police force, has him removed from the investigation. However, Date and Mizuki infiltrate Sejima's manor to enact revenge. Date fatally shoots Sejima and falls unconscious, but Mizuki saves him through a Psync. In the Annihilation route, Date fails to prevent Iris and Ota's murders. Meanwhile, Pewter reveals that the original Cyclops Serial Killers were two murderers, with one of them being Rohan Kumakura, a leader who seemingly died by suicide a year ago. #89 offers information to Date about Shoko's death, as well as sharing a story about his past life as an assassin for hire before falling in love with Hitomi. When Date Psyncs with #89 for more information, he finds Boss in his Somnium. Date later uncovers a video of Boss fatally shooting Sejima and incapacitates her when he finds her at Iris and Hitomi's home. After Psyncing with Boss, Date learns that she is possessed by Saito, Sejima's son and the other Cyclops Serial Killer. Saito reveals he had been using a stolen prototype of the Psync Machine to exchange bodies with Date's acquaintances and use each body to kill the previous one, with Iris, Sejima, and Boss being long dead. In addition, Date realizes that he is inhabiting Saito's body and that his original body is #89. Saito threatens him with Hitomi's safety in exchange for his body, and despite Date acquiescing, she is still killed.
Right side In the right branch, Date convinces Iris that she is in danger after seeing a dead body resembling her in Mizuki's Somnium. He discovers the body at a warehouse but sees Iris inexplicably alive the next evening. Iris speculates that Date may have jumped into a parallel world where she is alive after saving her in Sejima's Somnium. Renju goes missing after a car accident, but he is later seen helping #89 escape during his interrogation with Date. After several kidnapping attempts, Iris insists she is being targeted by the secret society Naixatloz. In Iris's route, Date believes her, and when she collapses, he takes her to the prototype Psync Machine, believing he is able to revive her through Psyncing, but she dies. In the Resolution route, Date refuses to believe Iris. He learns from Hitomi that Iris has a brain tumor, which causes her to hallucinate, and she is expected to die by the end of the year. When she goes missing, Date finds the same dead body in the warehouse again, but Aiba identifies the body as Manaka, a classmate of Hitomi and Renju's. Hitomi confesses to Date that, 18 years ago, Manaka had an affair with Sejima and was murdered by Saito. This led to Hitomi raising her baby, Iris. Saito, in #89's body, kidnaps Iris and Hitomi as hostages and uses the prototype Psync Machine to force Date into returning into their original bodies. Date recalls his past as #89: he had initially used the Psync Machine to switch bodies to protect Hitomi and Iris, but this inevitably led him to investigate the original Cyclops Killings; once Saito discovered the truth, he had forced Date to switch bodies with him, and a malfunction caused Date to lose his memories. Alerted by Aiba, Date's friends intervene and save him and Iris. When Saito threatens to shoot Hitomi, Date orders Aiba to self-destruct, killing Saito and destroying the last of her data. Three months later, the police pays for Iris's tumor treatment, and after she recovers, Date takes her around town to pay respects to their friends. Boss secretly has Pewter reinstall Aiba in Date's left eye, who is revealed to have survived by recompiling her personality in the
cloud. ==Development==