Iris is a 17-year-old high school senior who desires a normal life after a traumatic childhood event. Ten years ago, she and her older sisters went missing for a month, returning with white hair, black eyes, and an insatiable hunger. As the youngest, she is introverted and studious, preferring to avoid conflict and stick close to her mother. When her sister Grey goes missing again, Iris finds herself forced out of her comfort zone to search for answers.

Vivi is the middle child of the Hollow sisters and plays bass in a punk rock band. She hides her beauty behind a rebellious exterior characterized by tattoos, piercings, and aggressive behavior. Like her sisters, she possesses strange physical traits and powers resulting from their childhood disappearance. She acts as Grey's fiery counterpart and fiercely protects Iris from anyone who threatens them.

Grey is the eldest Hollow sister and a world-famous model and fashion designer. She creates heavily stylized clothing that incorporates items like bones, dried flowers, and secret messages. Confident and unapologetic, she embraces the strange powers she and her sisters share, often using them to manipulate others. Her sudden disappearance forces her sisters to uncover the dark secrets she keeps hidden in her covert apartments.

Cate is the mother of the Hollow sisters and works as an emergency room nurse. She is fiercely protective and highly anxious, tracking Iris's location constantly via a phone app. Her desperate need to understand what happened to her daughters during their missing month drives her to hire private investigators every year. She heavily favors Iris while harboring deep resentment toward her eldest daughter.

Gabe was the gentle carpenter father of the Hollow girls. Following his daughters' return from their month-long disappearance, his mental health rapidly declined. He became increasingly paranoid, insisting that the girls who came back were not his real children due to their physical changes and strange behavior. His handwritten journals document his terror before his death by suicide.

Tyler is a successful Korean British model known for his eccentric fashion sense, including floral suits and lipstick. He has been dating Grey for over a year but recently assumed they broke up due to her frequent, unexplained absences. He becomes reluctantly entangled in the search for Grey, bringing a dramatic but grounded perspective to the sisters' supernatural discoveries.

Agnes is a small girl living in an old house in an unknown, secluded location. She possesses extensive knowledge of the occult, portals, and the supernatural boundaries between life and death. She owes a debt to Grey and provides crucial shelter and healing when the group arrives injured and desperate.

Paisley is a 12-year-old student whom Iris tutors in computer coding. She is fascinated by the dark rumors surrounding the Hollow sisters, explicitly asking Iris if she is a witch. Her religious parents ultimately terminate the tutoring arrangement after learning about Iris's infamous family background.

Jennifer is a wealthy student at Iris's private school who typically ignores her. She participates in the social ostracization of Iris following a disastrous game of spin the bottle years prior. She suddenly feigns kindness to Iris solely to gain access to the glamorous world of Grey and Tyler Yang.

Justine is Iris's primary bully at her private school. She actively tortures Iris with cruel pranks, such as leaving dead birds in her locker and photoshopping her face onto images of burning witches. She harbors a deep fear and hatred of the Hollow family after an incident where Grey and Vivi forced her to shave her own head.

Yulia is a makeup artist and one of Grey's former roommates. Years ago, she attempted to follow Grey during one of her mysterious disappearances and vanished for a week. She returned deeply traumatized, covered in bloody runes, and now suffers from nightmares about the dead.

Rosie is Tyler's older sister who died in a tragic drowning accident at the age of seven. Tyler was caught in the same riptide and survived, leaving him with profound survivor's guilt. Her memory casts a long shadow over Tyler's life and motivations.