Luomen is a secondary character in The Apothecary Diaries. He is a disowned member of the La clan, a former imperial court physician who was made a eunuch, and now works as an apothecary in the red-light district. He is the adoptive father, biological great-uncle, and mentor of Maomao. In his youth, he was a genius in both Eastern and Western medicine, trained as a court physician. His extreme bad luck repeatedly turned his kindness into tragedy. He was ordered to prioritize the birth of the previous emperor's child over that of the current emperor's consort, Ah-Duo. Due to complications, Ah-Duo lost her uterus and her child later died after being fed honey. Luomen was held responsible for these accumulated misfortunes, was punished by having his kneecaps removed, and was banished from the imperial palace as a criminal. He settled in the red-light district, where he lives quietly as a physician for the Verdigris House brothel and its courtesans.

Personality-wise, Luomen is kind, humble, calm, patient, and gentle with both patients and pupils. He rarely shows anger, even when treated unfairly. His demeanor is so soft that Maomao compares him to a kind grandmother. He is portrayed as a pushover and passive to the point of being taken advantage of. However, he possesses extremely sharp powers of observation and a penetrating diagnostic eye, allowing him to see through symptoms, lies, and human behavior. Despite his mild exterior, he can be firm when necessary, showing hidden resolve and a willingness to use his influence within his clan to protect those he cares about.

His primary motivation is the well-being of his adoptive daughter, Maomao. He taught her everything she knows about medicine and writing to ensure she could have a career outside of prostitution. He supports her independently and trusts her abilities, intervening only when he believes her life is in danger. He is motivated by a quiet desire to protect others, especially the vulnerable women of the pleasure district, using his medical knowledge to serve a marginalized community.

In the story, Luomen serves as Maomao's foundational influence. His teachings and values are the lens through which she approaches problems. Though he remains mostly out of public view, his intelligence influences the plot. He is the reason Maomao has her vast knowledge of poisons and medicine, which she uses to survive in the imperial palace. He reappears later in the story when his skills are needed, returning to the rear palace as a temporary physician to assist with a difficult birth.

His key relationships are with Maomao, whom he loves and respects deeply, and with Lakan, the eccentric military strategist and head of the La clan. Luomen is Lakan's uncle, and the two have a complex dynamic. Lakan respects Luomen greatly, and Luomen is one of the few people who can put Lakan in his place. This relationship becomes crucial when Luomen uses his influence to compel Lakan to act to save Maomao. He also has a past connection to the emperor, having performed a cesarean section for his birth.

Development-wise, Luomen is a character shaped by tragedy and resilience. He was a brilliant physician whose life was derailed by a series of cruel coincidences. He accepted his punishment and exile with humility and did not seek revenge. His arc is about the quiet endurance of a good man who continues to serve others despite his own suffering, and his influence is felt through Maomao's actions.

Notable abilities include his exceptional skill in both Eastern and Western medicine, including the ability to perform cesarean sections. He possesses a deep understanding of pharmacology, toxicology, and human physiology. His diagnostic abilities are keen, allowing him to identify ailments and uncover hidden truths with minimal information. He is also a patient and effective teacher, having instilled in Maomao a rigorous, principle-based understanding of medicine rather than mere memorization.