The series details the life and history of Nanako Shichigusa, a 16-year-old who works as a maid (not nurse as the title might imply) in the hospital of Dr. Kyogi Ogami, the male lead. Nanako is a classic ditzy slapstick protagonist who tends to accidentally break things and do everything wrong. Ogami treats her frequently in a cruel or heartless manner -- threatening her, yelling at her and even subjecting her to physical abuse -- yet at the climax of every episode he comes through to rescue her from whatever predicament she has gotten herself into. Much of the series revolves around the relationship between Nanako and Ogami -- his mean veneer, her faith in him, and how he alternates between the evil mad scientist archetype and the knight in shining armor archetype.
As the series progresses we are gradually revealed the history between Nanako and Ogami\'s family and given a reason why the two are so tightly knit together, as well as why the title refers to Nanako as a \"nurse\". A minor supporting cast is introduced, though Nanako and Ogami are clearly the leads. The plot incorporates the American military, the Catholic Church and outlandish science fiction experiments, with these elements progressed mostly in the lead episode and the last two episodes. The middle episodes 2-4 feature mostly unrelated one-shot plots, though minor progress is made in each episode regarding the history between Nanako and Ogami\'s family.
In the beginning, Nanako was the subject of a cyborg experiment conducted by Dr. Ogami for one of his most powerful robots. Through rigorous training, Dr. Ogami trained Nanako to withstand the pain. However, he made her too strong, and the plan ultimately failed. However, recent developments between the Pentagon and the Vatican to resurrect Jesus for the Second Coming have landed Nanako as the subject of an operation in which she will give birth to the new Jesus.
Throughout the series, we learn that Nanako is, in fact, the third clone in a series of clones cloned from the original Nanako. The original died from a mysterious illness, and an experiment to clone her was successful. However, around the age of 20, each Nanako clone dies of the same mysterious illness that claimed the life of the first Nanako. It has been Dr. Ogami\'s quest to cure the \"Nanako illness\" ever since he promised the second clone that he would heal her before she died when he was young