Mai Oume is a central ally in the Shinkalion Change the World narrative, introduced as a second-year junior high school student who shares a long-standing friendship with the protagonist, Taisei Onari, and his rival, Ryota Kuzuryu. She is a student at Shinkai Academy, where she is affiliated with the railway club, and she is also connected to the operations of the Evolutionary Railway Development Organization.

In terms of personality, Mai serves as a confident and outspoken counterpart to the more reserved Taisei. She is characterized by her ability to speak her mind clearly, set her own goals, and communicate effectively without hesitation. She is fundamentally a kind-hearted individual who willingly offers her support to others, particularly assisting Taisei with his personal challenges. Her most defining trait is a deep and genuine passion for advanced technology, with a specific focus on railway infrastructure. This enthusiasm is so pronounced that she feels great joy upon learning that the artificial intelligence unit Vina was developed by Taisei's older sister, Ina Onari, whom Mai holds in high regard as a genius engineer and a personal idol. Her excitement grows considerably following Ina's return to the organization, as she cherishes the opportunity to work alongside the person she admires so much.

Her role in the story is primarily that of a non-combatant. Unlike the Shinkalion drivers who engage in direct battle, Mai operates from a support capacity. She focuses on providing moral support to the pilots, caring for their well-being, and demonstrating a keen determination to solve problems when crises arise. Her familiarity with railway technology and the organization's systems makes her a competent and reliable presence during operations.

Regarding key relationships, Mai has a complex dynamic with her two childhood friends. With Taisei, she is patient, helpful, and encouraging, often working to assist him in his endeavors. In contrast, her relationship with Ryota is marked by a sharp lack of patience. Because she has known him since childhood, she is intimately familiar with his quirks and annoying habits, and she frequently reacts to his antics with physical reprimands. This close history also makes her acutely aware of Ryota's hidden jealousy towards Taisei, a feeling he refuses to admit aloud.

The character experiences some development throughout the series, though her role as a support staff member sometimes limits her screen time in active combat scenarios. A significant plot point involves her being kidnapped and placed under the control of an antagonistic force, a situation that becomes a primary motivation for her friends to rescue her and return her to normal. Her deep connection to the technology is highlighted by a unique ability: she is said to be capable of connecting to the metaverse, a skill that makes her a target for those seeking to create new technological systems.

In terms of her capabilities, Mai possesses no piloting abilities for the Shinkalion robots. Instead, her notable abilities lie in her technical knowledge of railway systems and her capacity for emotional intelligence, which she uses to support the drivers from the sidelines. She is described as having brown hair that reaches chest-length and brown eyes.