Nancy is a 17-year-old girl who recently returned from an Underworld called the Halls of the Dead. She has bone-white hair streaked with black and wears strictly black-and-white clothing, directly rebelling against her parents' attempts to force her into bright, cheerful outfits. Nancy values extreme stillness and quiet, finding the modern world overwhelming and longing to return to the dark, peaceful domain she considers her true home.

Jill is a 17-year-old girl who spent years in the Wicked world of the Moors alongside her twin sister, Jack. In sharp contrast to her sister's scientific pursuits, Jill favors pastel dresses and carries a parasol, maintaining the delicate appearance preferred by her vampiric mentor. She harbors a desperate, intense need to return to the Moors, causing her to view her peers and circumstances with deep resentment.

Jack is a brilliant teenage scientist who studied under a reanimator in the Wicked world of the Moors. She has blond hair, often wears a biohazard-patterned bow tie, and approaches emotional situations with cold rationality to shield her vulnerabilities. Despite her intimidating demeanor and morbid interests, she is fiercely protective of those she allows into her inner circle.

Kade is an 18-year-old transgender boy who spent three years in a Fairyland called Prism before being banished upon the discovery of his gender identity. Rejected by his biological family, he views the boarding school as his permanent home and takes on quiet leadership responsibilities. He manages clothing exchanges among the students and is fiercely protective of his peers and the school's legacy.

Eleanor is the founder and headmistress of the Home for Wayward Children. Although almost 100 years old, she appears to be in her sixties due to the longevity granted by her childhood travels in a Nonsense world. She presents a respectable, mundane front to parents while secretly providing a sanctuary for world-walkers, a dual life that places a heavy emotional burden on her.

Sumi is a student who lived in the Nonsense world of Confection. Once a sad-eyed girl trapped by stifling expectations, her time in a magical world transformed her into a vibrant, outspoken teenager. Because her biological parents are deceased, she lives at the school permanently as Eleanor's ward, hiding her vulnerability behind a cynical attitude about hope.

Lundy is the school's group therapist and Eleanor's right-hand woman. Due to a bargain made in the Goblin Market, she physically ages backward and resembles an eight-year-old girl despite being a grown adult. She takes a blunt, realistic approach to counseling, believing that giving students false hope about returning to their worlds is cruel.

Loriel is a student who spent time in Webworld, a land ruled by spiders, which honed her remarkably keen vision. She is eager to return to her portal world and frequently roams the school grounds searching for her missing door. She harbors a strong prejudice against students from Wicked worlds, leading to tension within the student body.

Christopher is a boy who traveled to the magical Country of the Bones. He possesses a special bone flute that allows him to communicate with skeletons through music inaudible to the living. He is cooperative, perceptive, and dedicated to helping his friends face the mysteries and dangers plaguing the campus.

Angela is a student who traveled to what she considers a "good, respectable" world. She represents the faction of the student body that looks down on those from Underworld or Wicked worlds, using prejudice and exclusion to cope with her own displacement from her portal home.

Seraphina is a student at the school known for her beauty and her connection to a portal world her peers deem "good." Her presence highlights the social divides within the school, as she sits comfortably among the more accepted and glamorous students.

Dr. Bleak is a "mad" scientist who resides in the Wicked world of the Moors. He served as Jack's mentor, teaching her how to reanimate the dead and giving her the freedom to explore her brilliant intellect without judgment or societal constraints.

The Master is a vampiric lord in the Moors who kept Jill as his darling companion. He prefers his associates to wear pale colors that show bloodstains and uses isolation to maintain complete control over those devoted to him.

The Lord of the Dead is the ruler of the Halls of the Dead. He values absolute stillness and taught Nancy how to survive in his domain, eventually insisting she return to Earth to ensure she truly wanted to stay with him forever.