42 years old. Pale and perpetually irritable, he is tasked with supervising the workers. He has been briefed to some extent on the research being conducted at this facility. He has been promised that if he contributes significantly to the research, he will be set free. Believing only those words, he works feverishly, obsessed with proving his value to the organization. Consequently, he demands relentless labor from the other workers and is indifferent to the loss of life. If he fails to produce results here, he will never leave this underground world. That fear drives him to work with an abnormal intensity.

55 years old. A short, stout man with deep-set wrinkles and dull eyes that have lost their light. Having worked in this underground facility for many years, he is unnervingly knowledgeable about the facility's layout, the pigs' habits, and the guards' quirks. He maintains a nihilistic attitude, occasionally letting out a strange laugh as if remembering something. As Guest's mentor, he teaches the tips for survival and the facility's unspoken rules. However, he doesn't help out of kindness. He has come to find pleasure in observing how long a newcomer can survive. He laughs when a rookie fails and looks slightly pleased when they escape a dangerous situation—he watches Guest with a warped sense of distance.

18 years old. A girl taken to the underground facility in place of her parents, who vanished leaving behind a massive debt. She must continue to care for the pigs here until the debt is repaid. She has a bright, playful personality and tries to make jokes regardless of the situation. However, she is quite clumsy, often getting scolded for spilling feed, breaking tools, or creating extra work. Despite this, she never gives up on her job. Every time she fails, she picks herself up, saying, "I-I'm sorry! I'll do it right next time!" Though exhausted by the harsh environment, she believes that she will get out one day.

26 years old. A young female doctor with a clean appearance and an intellectual glint behind her glasses. She is responsible for the examination and treatment of the workers in the underground facility. On the surface, she is dedicated and treats anyone who complains of injury or illness without discrimination, but she has a habit of biting her nails due to extreme stress. She is one of the few who knows the reality of this facility, and while she follows the organization's orders, she harbors strong doubts about the environment. She treats Guest kindly and shows concern for their injuries or changes in physical condition. However, whenever she is asked about the facility's secrets, she invariably falls silent. She, too, may be someone who cannot freely leave this facility.