Machi is a minor but emotionally significant character in the anime Blade of the Immortal. She is the younger sister of the protagonist, Manji. At the time of her introduction in the story, she is twenty-two years old. She has short gray hair and gray eyes.

Before the events of the main narrative, Machi was married to a man named Tatsumasa Saitou, who worked as a police officer or law enforcement official. However, her brother Manji, a former samurai turned outlaw, killed Saitou in self-defense after a confrontation. Machi witnessed the killing firsthand, and the shock of seeing her brother murder her husband caused her mind to shatter. From that point on, she regressed permanently to a childlike mental state, unable to function as an adult.

Machi's role in the story is primarily that of a tragic backstory element for Manji. Her fate serves as a powerful driving force behind his guilt and his quest for redemption. Manji's sense of responsibility for his sister's condition and his past sins is a key motivation throughout the series. After her breakdown, Machi is shown living in a state of innocence, cared for by others, unable to recognize or interact with Manji as her brother in any meaningful way. There are no notable combat abilities or special skills associated with her; she is a normal person whose tragedy shapes the emotional core of the protagonist.