Sayuri Muranushi is a 19-year-old university student working part-time as a waitress at the Wagnaria restaurant. She possesses the unusual ability to see and interact with invisible customers, later revealed to be ghosts, despite her own firm disbelief in the supernatural. Her absence due to illness or studying causes disturbances among coworkers as the ghostly patrons become more active and disruptive.

Her personality exhibits minimal emotional expression, a trait inherited from her mother Saiko. She rarely smiles, and when she does, it often provokes unsettling reactions; one smile directed at coworker Masahiro Adachi traumatized him, causing him to faint whenever he sees it afterward. Despite her stoic exterior, she harbors feelings for Adachi, expressed through gestures like giving him handmade chocolates and cookies.

A significant backstory involves her consuming Hana Miyakoshi's poisonous chocolate after losing a game of rock-paper-scissors a year prior. This led to a near-death experience where she "met St. Valentine". This event influences workplace dynamics, particularly around subsequent Valentine's Days when her chocolates cause Adachi to faint.

Her character development unfolds through interactions with Adachi. His attempt to apologize leads to a visit during her illness, revealing her complicated relationship with her mother and prompting a rare emotional response. Later, she initially misunderstands his request for a date as a prelude to breaking up. This confusion resolves when Adachi clarifies his intentions, leading her to smile genuinely at him without triggering his trauma.

Her family background provides context; her mother shares her emotionally restrained nature. Their interactions during her illness highlight underlying familial tensions and affections.