Mami Yamaguchi is a minor supporting character in Thermae Romae. She works at a luxurious hotel and is instructed by her manager that an Italian guest is expected and she must attend to him. When the Roman architect Lucius Modestus unexpectedly emerges from one of the hotel's baths after one of his time slips, Mami mistakes him for the anticipated Italian visitor and promptly helps him. Her role in the story is brief and primarily serves to facilitate Lucius's introduction to the modern Japanese setting during one of his accidental travels. She is a hotel employee who is dutiful, polite, and professional, carrying out her work responsibilities without question. Her personality is not explored in depth due to her limited screen time, but she demonstrates a willingness to assist and a calm demeanor when faced with the unusual situation of a man appearing from a bath she was not expecting. Her motivations are straightforward: she is simply doing her job as instructed by her manager. She has no significant development across the series, as she appears only in a single scene and does not reappear. Her key relationship is with Lucius, whom she treats as a guest, and with her manager, who gives her the directive. She has no notable abilities beyond her role as a hotel staff member. Her primary function in the narrative is to act as a bridge between Lucius's arrival and the modern Japanese environment, allowing the story to proceed with its comedic and cultural contrast themes.