Kojiro Kitahara is a third-year student at the Kirishina Science and Technology Academy High School. He serves as the aircraft designer for the Advanced Technological Development Department, Educational Development Class, known as A-TEC, making him responsible for the design of the team's prototype rockets. He is one of the few male students in the class.

His personality presents a noticeable duality. Kojiro often acts with a maturity that surpasses his classmates, presenting a composed exterior within the workspace. Beneath this surface, however, he possesses a nebulous and frivolous character. He has a tendency to cause trouble and exhibits a mildly sleazy or mischievous side, frequently engaging in lighthearted schemes and banter.

His primary motivations are driven by the collective goals of A-TEC. He takes pride in his technical work and is dedicated to the success of the team's projects, contributing his engineering skill to overcome the development challenges they face. His role within the narrative is that of a capable and steady supporting member of the group, providing some of the everyday high school realism that contrasts with the high-stakes corporate conflict.

Kojiro is close friends with the other male students in A-TEC, Sakugo Maioka and Subaru Yamaki, with whom he frequently spends time and causes minor trouble. He is also a contemporary of the third-year students Mizuki Sera, Iris Shirasaki, and Makoto Ryouke. He and Makoto often share the role of the logical straight man against the team's more chaotic tendencies. He respects Kaito Sera as a leader and engineer.

Kojiro does not undergo a dramatic individual transformation over the course of the story. His development is seen through his steady reliability and his consistent commitment to his teammates in the face of pressure. His notable ability is his talent for aircraft design, a specialized skill that is fundamental to A-TEC's engineering operations and their ability to advance their projects.