Nationalism
Sadao and Hana, as well as the other Japanese characters in the text, evince a high degree of nationalism (as does Tom, but he is a much less developed character). They are proud of their country, desirous of winning the war, committed to their cause, and disdainful of Americans. The servants are highly nationalistic and cannot fathom other considerations, such as the ethics of medicine, coming into play, whereas Sadao and Hana have cracks in their nationalistic facade because they feel a sense of compassion for the American boy that supersedes their perception of him as their enemy. Buck is condemnatory of nationalism when it completely obfuscates one's understanding of another's humanity; she also does not see it as something just the Japanese have, nor as something just the Germans have: all countries, including the United States, have a nationalistic, "the-other-is-the-enemy" mindsets.
Universal Humanity
Sadao and Hana might be devoted to their country and lacking in any real affection for Americans, who seem to have been consistently racist in their treatment of the Japanese living and studying among them (though they are not mentioned in this story at all, the Japanese internment camps come to mind), but they are still endowed with a higher level of compassion and ethics, and they know that their decision to save Tom's life even though he is their enemy is the right one, difficult though it may be. They can transcend nationalism to an understanding of universal humanity—not because they are saints, but because they are thoughtful and brave.
Medical Ethics and Duty
Sadao seems to be a doctor before he is a Japanese citizen, a husband, an employee, or someone at war. He knows the Hippocratic oath that says he has a duty to save a life, to put health before harm, and to see beyond borders, skin color, and the exigencies of politics, conflict, and war. He acts instinctively and intuitively, caring only about the viscera, the bullet, and the body—he isn't deterred by the fact that the boy he is working on is "supposed" to be his enemy. He is a consummate professional, his desire to save lives and heal permeating every fiber of his being.
