Hiraya is a 25-year-old medical student living in the shadow of family tragedy. Conceived as a genetic match to provide bone marrow for her chronically ill older brother, her entire early life centered around stringent health regimens and serving as a medical resource. Following his death in a car crash, she abandoned her true passion for songwriting and enrolled in medical school to live out his dream instead. Feeling purposeless, she boards the Elsewhere Express, where she discovers her discarded musical talents hold tangible, physical power.

Quentin is a celebrated portrait artist suffering from retinitis pigmentosa, an inherited disorder slowly reducing his vision to a pinhole. Haunted by his father's suicide and his mother's subsequent denial, he channels his lingering anger into his art, frequently painting scorched moths. Despairing over his impending blindness, he boards the Elsewhere Express and discovers his sight is miraculously restored. Desperate to keep his vision, he eagerly accepts the strange logic of the train while seeking a permanent place on board.

Lily serves as the conductor of the Elsewhere Express. She does not use her own face or name, instead borrowing identities from the daydreams of passengers in the waking world to appear more relatable. She enforces a strict bureaucracy, insisting that passengers drink a special memory-erasing serum to shed their excess emotional baggage. She believes this is the only way to prevent passengers from losing their grip on the train and becoming spectral Echoes.

Rasmus is the former conductor of the Elsewhere Express who currently serves as the acting archivist. Wearing a leather eyepatch, he balances his lonely duties with building intricate miniature crystal trains out of passengers' memories. Unlike Lily, he operates with a degree of flexibility, sometimes keeping secrets or bending the rules to protect the train. He possesses deep knowledge about the train's construction and history.

The stowaway is a hostile, destructive entity that terrorizes the Elsewhere Express. It operates as a physical manifestation of rot and decay, feeding on dark thoughts and spreading structural damage across the train's magical cars. Frequently appearing as a swarm of black moths, it brings impossible rain to the train and thrives on sorrow, forcing the crew to take drastic measures to isolate and destroy it.

Jace is Hiraya's deceased older brother. He suffered from thalassemia major, a severe blood disorder that dictated his family's every decision. Despite the clinical nature of their upbringing, he was a loving brother who often sneaked treats to his sister. His death in a sudden car crash while driving home to watch her perform left a permanent scar on his family.

Connie is Quentin's mother. After her husband died by suicide, she publicly stated that his death was an accident, choosing to preserve their social standing over facing the truth. This decision permanently fractured her relationship with her son, who resents the false smiles and lies she employs to cope with her grief.

Dev is a photographer who works for the train's maintenance department. His primary job involves gathering discarded songs, which manifest as glowing orbs, and utilizing their specific emotional resonances to repair damaged sections of the train. He quickly spots Hiraya's natural talent for handling these musical repairs.

Astrid is a painter aboard the Elsewhere Express responsible for crafting the skies and oceans for the train's lower compartments. She explains the high stakes of creation on the train to new passengers, requiring them to sign safety waivers because dark thoughts can easily conjure dangerous reality.

Olly works as a sous chef on the train but remains in a nearly catatonic state. He previously wandered through a locked door into the Missed and Misplaced Department, losing large fragments of his mind and memories before he was finally retrieved. He draws unsettling spiral shapes in notebooks, hinting at the depths of his trauma.

Mr. Goh is the pharmacist of the Elsewhere Express. He distills a specialized, black memory-erasing serum from a poem. This tonic is distributed to passengers to help them shed their emotional burdens, ensuring they remain light enough to stay aboard the train.

Han is the curator of the Gallery car, which houses an outdoor water garden and a unique reflection pool that trades passengers' secrets for gossip. Because she consumed the train's memory-erasing serum, she has no recollection that she was once engaged to Rasmus in the waking world, and is now married to an alternate version of him.

Manon is an independent perfumer who refuses to take Mr. Goh's memory-erasing tonic. Operating in secret, she crafts forbidden fragrances distilled from distinct memories and raw emotions. She believes that holding onto the sensation of loss is essential for appreciating life.

Alain works as a boatman in the transient environment of the Wandering City. He deals in unusual currency, charging passengers in questions rather than money, and acts as an operative fetching unique emotional scents for Manon's secret perfumery.

Abbie is a mechanical spider who functions as the true Archivist of the Elsewhere Express. Because mechanical beings cannot have their memories erased by Mr. Goh's serum, Rasmus keeps her confined to a jar to prevent her unedited recollections from causing the train's thought-architecture to crack.

Aki is the bartender stationed at the Lotus Lounge, an establishment located inside a giant flower under a purple sky. He bears the same shimmering eternal knot on his palm as the passengers, confirming his bond and subservience to the train.

Isla handles the accommodations for passengers aboard the Elsewhere Express. She manages room assignments and distributes compartment keys, strictly adhering to the bureaucratic procedures governing the train's living quarters.