Sano Etsuko was the mother of Sano Ichirō and the wife of his father. She resided with her husband and her maid Hana at the house near the Sano Martial Arts Academy, and continued to do so after his death.
Etsuko's name is not given in this novel, rather she is referred to throughout as Sano's mother. She is first seen attending to her sick husband in the house, where she displays an optimism that seems not to coincide with the reality of her husband's illness. She disappears from the room where her husband is resting to go and prepare a meal. Later, after Sano has been let go from his position as a yoriki, he returns to his parents' home to inform them of what has happened. Etsuko is surprised by this as he should be on duty. When Sano reveals why he is there, his mother tries to play peacemaker between Sano and his father, when his father turns a ways from him in disgrace upon hearing his son is no longer working as a yoriki. Sano leaves the house despite his mother's entreaties. After Sano has saved the shogun, he returns to the house where his parents live, and inform them of his good fortune and that he will now be living in Edo Castle as the special investigator to Tokugawa Tsunayoshi. Etsuko is overjoyed at this, and is happy her son has found such good fortune.
Etsuko is mentioned briefly as Sano states that when he moved to Edo Castle, he brought his mother and her maid with him to live with him in the castle. His mother was so unhappy however that Hana convinced Sano to let his mother return to her old home near the Academy, as she would be happier where she had spent so much time. Sano reluctantly lets her return home. Later, she attends the miai meeting between her son and Ueda Reiko.