Sara Haizaki is one of the two concierges working at the Hotel Inhumans, an establishment that caters exclusively to assassins and other underworld figures. She serves as a central figure in the story, operating alongside her colleague, Ikuro Hoshi. Information about her life before joining the hotel is largely a mystery, including her exact age, though she has a youthful appearance. Her professional reputation is formidable; she is widely recognized as the most powerful Gatekeeper and protector of the hotel, and her presence alone is known to deter potential trouble from guests and outsiders alike.

In terms of personality, Sara is characterized by her remarkable emotional control. She maintains a cool, unreadable poker face while on the job, very rarely letting her feelings slip in front of others. On the rare occasions she does allow herself a small smile, it stands out as a significant event due to its infrequency. Despite her stoic and ruthless professional demeanor, which can come across as cold, she has a surprisingly light-hearted side to her private life. Her favorite hobby is watching comedy duos, as laughter is one of the few things that truly allows her to relax.

Sara’s primary motivation appears to be the flawless execution of her duties. She and Ikuro are bound by the hotel's core principle of never refusing a guest's request, no matter how dangerous or morally complex. She approaches this task with a calm, professional dedication, serving as a quiet comforter and a source of unwavering logistical and physical support for the assassins who seek refuge in the hotel. Her role in the story is therefore to be the anchor of the Hotel Inhumans, providing the strength and stability that allows the establishment to function and the various guest narratives to unfold. She handles the physical protection of the hotel and its clients, while Ikuro often handles research, though Sara is clearly the superior in their working relationship.

Sara's key relationships are primarily professional. She works most closely with Ikuro Hoshi, a newer and more naive concierge who is uncomfortable with the violence and bloodshed inherent in their workplace. While she is his senior and acts with great authority, their dynamic is one of partnership in service to the hotel’s guests. She also interacts with the various assassins who stay at the hotel, fulfilling their requests without judgment. Over the course of the series, Sara undergoes subtle development. While she begins as an almost impenetrable figure of strength and neutrality, the compassionate and empathetic lessons learned through the stories of the hotel's guests appear to resonate with her, suggesting a gradual transformation in her own understanding of humanity and identity.

Sara possesses notable abilities that make her a legend among both colleagues and guests. Her most famous skill is her unmatched combat capability. She can single-handedly face multiple armed opponents, even those wielding firearms, and subdue them effortlessly using only her personal knives or whatever objects are at hand. Her appearance provides a tactical advantage; she has strikingly long, blonde hair that she usually ties back in a ponytail with a unique hairpin that secretly contains a hidden knife. In her private life, she lives alone except for a beloved pet cat, and she shows no interest in fashion, preferring simple and comfortable clothing when off duty. A testament to her legendary work ethic, it is said that she has never taken a single day of paid leave since she began working at the Hotel Inhumans.