Ikurou Hoshi despises killers, yet he works as a concierge at a hotel that caters exclusively to assassins. Alongside his colleague Sara Haizaki, a cool-headed and highly skilled fighter, he serves the dangerous clientele of the Hotel Inhumans. The establishment provides every service its guests could desire, from fine dining and entertainment to weapons procurement, false identities, and discreet corpse disposal. While Sara handles security and guest requests with professional detachment, the reluctant Ikurou handles research into the backgrounds of the patrons he claims to loathe.

The story unfolds primarily through the eyes of these two concierges as they interact with a revolving door of contract killers. The hotel serves as a neutral sanctuary where hitmen from various backgrounds can seek respite. The narrative is largely episodic, with each request focusing on a different guest. One early story follows Siao, a young man who was forced into a life of killing to protect his sister, only to suspect betrayal by the organization that holds her captive. Another arc features a salaryman who disguises himself as his targets, while a particularly poignant tale involves an elderly assassin suffering from dementia who checks in for one final, tragic job.

As the series progresses, Ikurou’s rigid moral opposition to murder is challenged. Despite his daily threats to quit, he is forced to witness the unexpected humanity within the killers he serves. He encounters assassins who kill to save family members, those who treat murder as a mundane office job, and others seeking redemption or revenge. Through these interactions, he learns the complex motivations and tragic pasts that led individuals to this underworld profession, blurring the line between monster and man. Notable recurring staff include the hotel's eccentric doctor who enjoys obtaining autopsy permissions and a tailor who believes fine clothing is key to happiness.

The season concludes with a multi-episode arc exploring the pasts of the lead concierges themselves. This storyline delves into the history of the hotel and the circumstances that made Sara the formidable guardian she is, while forcing Ikurou to fully confront his own place within the world of the Hotel Inhumans. Rather than glorifying violence, the series focuses on the mundane sadness and emotional weight carried by its characters, framing assassination as a grim profession rather than a glamorous one. The first season completed its broadcast run, and production for a second season was subsequently confirmed.