In the distant future, KAI is an unassuming, soft-spoken, 19 year old recruit who unwittingly aced his selection examinations into the army’s elite force, the Mecha Corps-Earth.
There is a reason for his proficiency in the Mecha subject. KAI’s father was a captain in the Mecha Corps. As such, from a young age, KAI was exposed to the world of robotics. KAI’s father would take the young KAI along for field trips and tell him stories about the history of mankind’s space missions, how the moon and Mars colonies came to be, and how war erupted when the leaders on Mars decided to exert totalitarian control over everyone. To KAI, the part he enjoyed most, was hearing about his Dad’s battles with the Mecha forces of Mars.
KAI’s toys were scaled robot model kits, and his dad would teach and help him make modifications to the robot kits, while sharing about how the robots will react to their pilots’ instructions. However on the day that the Mechs from Mars sprung a surprise attack on Earth, KAI's father evacuated everyone from their home before joining the battle. This was the last time KAI ever saw his dad. The young KAI and his mother, who narrowly survived the unexpected attack, relocated their family home to the countryside.
KAI always believed that he will see his dad again, as he was never reported dead, but Missing-In-Action. This spurred his interest and determination to join the war and hopefully get to see and perhaps rescue his dad from the human base on Mars.
Despite having intellectual knowledge about the robots, KAI being small-built, lacked the physical strength of a typical Mecha Corps pilot. He even concealed a secret in order to pass the medical examinations- He has childhood asthma. For what he lacks in size, KAI makes up for it in perseverance. He decides to overcome this by building his physique, and building a relationship with his robot. He remembers the advice from his dad, that the strongest Mecha robot in battle is one where the pilot and robot are thinking and fighting as one. However, not everyone in the Mecha Corps believes in this philosophy and many see the robots as mere mechanical tools.