Kana Ushiro is a central character in the story, known primarily as the ten-year-old sister of Jun Ushiro. She is part of a group of children who are forced to pilot a giant robot named Zearth to defend their world, with the cruel stipulation that each pilot dies after their single battle. Kana's background is deeply intertwined with her family's complicated dynamics. She and Jun are not related by blood, a fact that creates underlying tension within the family. Despite this, she is portrayed as a gentle and caring younger sister, seemingly the most innocent member of the group.

Regarding her personality, Kana is depicted as a kind and thoughtful child who wishes for her fractured family to do the right thing and find reconciliation. However, she also struggles with significant anxiety and fear. Early in the story, she becomes withdrawn and distant, burdened by a secret she is terrified to share. This secret is that she has a debilitating illness and only has a short time left to live. This knowledge compounds the horror of her situation as a pilot, as she already faces a limited lifespan. Her primary motivation is not grand or strategic; rather, it is a personal desire for family harmony and acceptance. The revelation of her illness to her peers is a pivotal moment, as she feared it would make her appear weak, but instead, she is met with their kindness and support.

Kana's role in the story is tragic, as she is fated to become one of the pilots. Her narrative arc serves as a major turning point for her brother, Jun. While her own battle, when it comes, is disappointingly short and lacks the intense geopolitical stakes of other pilots' fights, it functions more as a catalyst for emotional growth in those she leaves behind. Her death, and the circumstances surrounding their family's secrets, steel Jun's resolve and transform him from an ill-tempered boy into a steely-eyed hero determined to face his own destiny. In this way, her significance in the larger story is defined less by her actions in the robot and more by the emotional impact of her life and death on her brother and the surviving pilots.

Kana's development is limited by her short time in the narrative. She is largely characterized by her quiet suffering, her secret illness, and her saintly wish for her family to overcome their dysfunction. As a ten-year-old girl forced to confront both a terminal illness and the responsibility of piloting a death machine, her story highlights the profound and often overlooked emotional toll on the youngest and most vulnerable participants in the conflict. She does not possess any notable combat abilities or special tactical genius; her fight is characterized by a few clever maneuvers, but the engagement is ultimately brief and overshadowed by the personal drama surrounding it. Her strength lies entirely in her emotional resilience and her capacity for love and forgiveness within a broken family.