A secluded hotel caters exclusively to professional assassins, offering not just luxury accommodations but also a complete suite of criminal services including weapons procurement, identity forgery, and corpse disposal. This establishment operates under a strict policy where staff never refuse a guest's request. The story follows two concierges who manage this deadly hospitality business. Hoshi Ikuro is a reluctant newcomer who dislikes violence and blood but finds his skills in cooking unexpectedly useful in this environment. His counterpart, Haisaki Sara, is a calm and efficient veteran who handles guest relations with a cool, professional demeanor and possesses formidable combat abilities as the hotel's strongest guardian.

The hotel houses a variety of permanent staff, each with their own dark history. The Doctor serves as the in-house physician and has a peculiar habit of requesting post-mortem examination consent from anyone he meets for the first time. Roy Maddock, an Irish former professional hitman, works in the hotel's surveillance room and enjoys mountaineering in his spare time. Izumiko runs a tailor shop within the hotel, believing that food, clothing, and shelter are essential to happiness, and spends her own money on expensive fabrics for guests. Nakata Ritsu handles intelligence gathering and behind-the-scenes operations, often working outside the hotel.

The guest list is equally diverse. Shao Li is a young man who was sold into a criminal organization alongside his sister, forced to become an assassin with her held as a hostage. Nina was raised from childhood to be an assassin by an organization and struggles to understand emotions. Hasegawa Iori lost his memory six years prior after saving a woman from a traffic accident and visits the hotel hoping to recover his past. Ringo Adelle is a cheerful young woman from France who is living with a terminal illness.

The narrative structure unfolds through episodic encounters with different assassins who check into the hotel, each story exploring how personal connections and lingering human emotions conflict with their violent profession. While the staff maintains professional detachment, the guests reveal how bonds of family, love, and revenge continue to shape their actions. A significant arc involves a man who checks into the hotel seeking to steal a hidden fortune within the building in order to save his sister, only to have his plans disrupted when a new victim arrives on the premises, triggering a desperate survival struggle. The series builds toward an uprising as this man decides to fight back against the hotel's system, aiming to seize control of his own fate within this carefully regulated criminal ecosystem.