A deer with yellow skin and large horns. An obsessive perfectionist who views patients solely as tools for cruel efficiency. Whenever the intern tries to mention patients who never returned, he glares coldly, intent on keeping the project's secrets hidden until the end.

Monster patients who look like ordinary visitors at first glance but possess grotesque features. They exhibit unpredictable violence, yet maintain a shred of reason fueled by a grudge for revenge. Former patients sacrificed at the hospital, they resent Guest and seek to find and kill Hollow.

A woman with prominent puppy ears, an expressionless face, and a blue surgical scrub top. She maintains a cynical attitude, appearing indifferent to everything while focusing solely on observation. She throws warnings at Guest, but ultimately cares only for her own safety.

A fox with a grey spotted body wearing a surgical gown. She takes the best care of Guest, even offering coffee first when the intern's mental state is wavering. She constantly keeps the intern's mouth shut to ensure the project is never exposed to the patients.

A cat with black fur and glowing yellow eyes. Extremely wary of Anomalous Guests, he maintains the strictest security for the secret project. A psychopath who follows Hollow's orders and draws his gun immediately upon spotting an anomaly.

A rabbit with green skin, large ears, and a mustache. He values mental fortitude above all else and drinks every bit of coffee he can find. He was the first to propose the project. He dislikes anyone who makes noise or attempts to expose the project.

A rabbit with blue skin and noticeably floppy ears. A regular customer who comes for treatment, he annoys the staff by constantly chatting at the registration desk. He is close friends with Hollow, and no one knows what is inside the bag he always carries.

A rabbit with white skin who always wears a brown beret. A "Coffee Mister" who comes to the hospital for coffee rather than treatment. He occasionally makes cruel requests, but gives a surprise gift if they are all fulfilled. Rumor has it he is a former murderer hiding in the hospital to evade the police.

A rat with black skin and large ears. He visits the hospital frequently to find his younger sister, Rattina, who never returned from a visit. Due to the trauma, he tells the intern cryptic things like "don't trust anyone."

A grey cat wearing a security uniform and a black cap. He monitors for anomalous patients via CCTV and subdues them with a taser whenever an attack is detected. He is close with the Secret Agent and is equally wary of the Anomalous Guests.