Akiteru Ōboshi, a second-year high school student, considers himself entirely ordinary, noting his physique is slightly more muscular than average from exercise yet firmly normal. He leads a disciplined life, prioritizing efficiency in academics, routines, and goals while actively avoiding romantic distractions. Despite this self-assessment, he harbors a driven secret: he is a game developer and de facto leader of the "5th Floor Alliance," a creative group collaborating on projects. This circle includes his only close friend, programming genius Ozuma Kohinata, and other talented individuals whose secret ambitions intertwine with his own.

His trajectory is significantly shaped by his family connection to Makoto Tsukinomori, president of the large entertainment company Honeyplace Works. To secure opportunities for the Alliance there, Akiteru agrees to his uncle Makoto's condition: entering a fake romantic relationship with Makoto's daughter, Mashiro Tsukinomori, who is also Akiteru's cousin and childhood friend. This arrangement thrusts him into a complex charade conflicting with his desire for simplicity and efficiency.

Relationship dynamics are central to Akiteru's development. He is initially annoyed by Ozuma Kohinata's younger sister, Iroha, due to her persistent intrusions into his personal space and relentless teasing; her behavior contrasts sharply with her kind, diligent honor student persona at school. However, a pivotal shift occurs after the "Ceremony of Knots" incident, where Iroha impersonates Mashiro. Trapped in a love hotel-like shrine setting, Iroha seriously confesses genuine feelings, causing Akiteru to perceive her as a romantic interest for the first time. Consequently, he starts finding her previously irritating behavior endearing and charming, often becoming flustered by her affection.

His interactions with Mashiro Tsukinomori are equally complicated. Their faded childhood friendship leads to a rocky reunion, marked by an accidental bathroom intrusion that makes Mashiro act coldly. The fake relationship further strains their interactions initially, though Mashiro later confesses her own genuine feelings. Akiteru demonstrates protectiveness towards her, confronting her past bullies during harassment. Navigating the pretense with Mashiro while managing growing feelings for Iroha causes significant emotional confusion, gradually shedding his initial emotional detachment.

Beyond his efficiency-focused facade, Akiteru exhibits strong loyalty and dependability within the 5th Floor Alliance. He supports members' dreams, like Iroha's secret ambition to become a professional voice actress despite family disapproval. His leadership involves mediating group dynamics and fostering collaborative creativity. Despite his insistence on averageness, he displays moments of perceptiveness and unexpected charisma that draw others to him, contradicting his self-image.

His name, Ōboshi Akiteru (大星 明照), means "big star" (大星) and "bright light" (明照), reflecting a contrast to his self-professed ordinariness.