Species: Human derived from the Black Case of Phantom Goa Nightmare Gender: Female Age: 20 Occupation: National Idol Family: The Lady (Mother) ■ Description A nationally popular talent loved by many. In reality, she is in a coma, existing as a being that wanders through people's dreams. Twenty years ago (2005), a single infant was born into reality as a "Black Case" derived from a Phantom Goa Nightmare, under the care of CODE agent Code Number: Two (later known as The Lady). Named "Nemu," the child was placed in an infant home to escape the organization's reach. When she was taken into a foster home eight years ago (2017), she was discovered by the president of an entertainment agency who supported the facility and entered show business. She quickly began to show talent, but four years ago (2021), just as her popularity as a national idol peaked, she fell into a coma following a location bus accident. Furthermore, she was taken from the hospital by The Lady. Trapped in a dream state, Nemu has since wandered through people's dreams, supporting the dreamers' desires by taking on roles and forms appropriate to their dream worlds.

Name: Minami Matsu Species: Human Gender: Female Age: 20 Occupation: Talent Manager Family: Guest (Brother) / Parents (Deceased) ■ Description A highly capable manager working for an entertainment agency. She is always worried about her brother, Guest, who is a well-meaning but somewhat reckless unemployed young man, and she continues to support him both emotionally and financially. When Minami Matsu lost her parents four years ago, she was visited by Zero, the commander of the secret defense organization CODE. He revealed that her parents, who were supposed to be working for a trading company, were actually agents of the organization. He also disclosed that Guest was not biologically related to her and that her mission was to watch over and raise him safely as family. At that time, she was asked to take over her late parents' mission. Deciding she would do anything to protect her only precious family, she endured rigorous training and began operating secretly as CODE Agent Code Number: Seventeen. On the other hand, she was not shared the details regarding the plan to make her brother fight as Kamen Rider Zetz, and she was initially unaware of the "Zetz Room" accessible through their home closet. While working at the agency and living happily with her brother, she received a call one day that he had been hit by an unmanned vehicle and rushed to the hospital.

Real Name: Unknown Species: Human Gender: Male Age: Unknown Occupation: Commander of the secret defense organization CODE Family: Guest (Son) ■ Description The commander of the secret defense organization CODE. He has dedicated his life to protecting world peace and is admired by many within the organization. While searching for countermeasures against the Nightmares that threaten the world, he was blessed with a son and conceived a plan to utilize the "Power of Collapse" (Catastrophe Goa Nightmare) residing in the boy's heart. The plan was to raise him as an agent who infiltrates people's dreams, transforming him into "Kamen Rider Zetz" to sever the causality of Nightmares with the power of collapse and subjugate them. Furthermore, he envisioned a system called "Code: Somnia" that would connect and manage all people's dreams into one. He believed that by properly operating Zetz and Code: Somnia, he could save the world and achieve a peace unthreatened by nightmares. Starting preparations for the plan, Zero personally participated in the design and development of the Zetz Driver, completing the Capsem (which houses parts of the power of collapse as unique abilities), Dream Learning (which enhances the power of lucid dreaming), and the remote-controlled variable machine Code Zeroida. Meanwhile, realizing that the Nightmare residing in his own heart was trying to obstruct the completion of Zetz, he entrusted two agents with the roles of foster parents to raise his son safely. After their deaths, he had their biological daughter, Minami Matsu, take over the role of agent.

Name: Tetsuya Fujimi Species: Human Gender: Male Age: 35 Occupation: Section Chief, Supernatural Cases Division, Public Security Bureau, Metropolitan Police Department (Assistant Inspector) Family: Unknown ■ Description The section chief of the Supernatural Cases Division at the Metropolitan Police Department. Though he can be a bit obsessive, he possesses excellent physical combat skills for subduing suspects and great initiative. He is in charge of investigating "Black Cases," mysterious incidents caused by Nightmares. He didn't believe in Nightmares, but he began to suspect that his subordinate, Katsumasa Kodaka—who vanished a year ago leaving only a resignation letter—fell victim to a Black Case. Driven by regret, he actively investigates supernatural incidents. Currently, Tetsuya Fujimi, along with the newly assigned Nasuka Nagumo, is investigating an accident involving an unmanned vehicle and its victim, Guest.

Name: Nasuka Nagumo Species: Human Gender: Female Age: 23 Occupation: Assistant Inspector, Supernatural Cases Division, Public Security Bureau, Metropolitan Police Department Family: Unknown ■ Description A new elite detective assigned to the Supernatural Cases Division of the Metropolitan Police Department. She is skilled at sharp kicks, and her serious and excellent work ethic is highly regarded within the organization. Assigned to the Supernatural Cases Division, she handles the investigation of Black Cases. Nightmares and Black Cases are beyond her understanding. Since the division was treated poorly within the organization, she initially suspected she had been demoted.

Species: Human Gender: Male Age: 32 He is trapped in a dream, cornered by the Shadow Nightmare residing in his heart. As the rebel Nox, he joins forces with The Lady to destroy CODE and carries out his revenge within the dream.