Ayame Yomokawa is the seventeen-year-old eldest daughter and heir of the Yomogawa family, the ruling house of the station of Aragane. Following the station's fall to the Kabane, she becomes the leader of the refugees aboard the armored train, the Iron Fortress, and is the holder of its master key, which grants control over the vehicle.

Initially, Ayame possesses a gentle and warm personality, treating others with sincerity and without the arrogance often associated with her noble status. However, she is also portrayed as inexperienced, insecure, and lacking in decisive leadership skills. In the early stages of the crisis, she is shown to be passive, easily influenced by the strong-willed retainers around her, and struggles to command authority in a state of chaos, even remembering the names of individual warriors. Her primary motivation is the protection of her people, believing that order exists to safeguard human lives, not to oppress them. This principle drives her actions as she grows into her role.

Ayame's role in the story is that of the Iron Fortress's commander and a central figure of human authority. Her position is crucial in deciding the fate of the Kabaneri, Ikoma and Mumei, on the train. Unlike many other humans who are driven by fear and prejudice, Ayame recognizes that she and her people owe their survival to the two Kabaneri. A key moment in her development occurs when she publicly tests Ikoma's loyalty by stabbing him with a dagger, demanding he bite her to prove he is not a mindless monster. This reckless but bold act demonstrates her willingness to take extreme measures to unify her people and quell internal strife. Her most significant act of resolve comes during a desperate battle against a powerful Kabane known as a Wazatori. To empower a blood-starved Ikoma, she cuts her own wrist and forms a blood contract with him, declaring that she will give her blood in exchange for him fighting the Kabane. This act marks a turning point, after which she firmly takes command, reclaims authority from her hesitant retainers, and officially decrees that the Kabaneri will be protected and provided with blood.

Her key relationships include her loyal and skilled bodyguard, Kurusu, who is protective of her and supports her development as a leader. She also shares a bond of trust with the Kabaneri hero Ikoma, believing in his humanity and sense of justice even when he is a threat to her. Ayame undergoes significant development, transforming from a passive, uncertain noble daughter into a resolute and dignified commander. By the events of the film Battle of Unato, she has matured into a decisive leader who can take command of allied forces and inspire others, proving her growth as a formidable leader in her own right. In terms of abilities, Ayame is a skilled archer. In combat, she wields a powerful, large-scale steam-powered bow that fires arrows with enough force and speed to pierce the heart cages of Kabane.