Eita Akutsu is the male protagonist of the story, known as a shy and introverted mechanical enthusiast or mecha otaku who leads a solitary life in his apartment. At school, he is described as gloomy, friendless, and a virgin, harboring a secret crush on Makina Agatsuma, the cheerful and popular gyaru classmate who seems to exist in a different world from his own. Despite his awkwardness and lack of social confidence, he dedicates significant time to honing his skills in robotics, a passion that defines much of his daily existence.

Eita possesses a genuine and deep-seated compassion for machines, which serves as the primary catalyst for the central plot. One night, he returns to his apartment to find the injured Makina waiting by his door. She reveals her true nature as an advanced android, and due to his demonstrated kindness towards a small robot earlier, she trusts him with her secret. Displaying remarkable mechanical aptitude, Eita is able to repair her and even trigger a self-regeneration feature for her synthetic skin, despite her radically advanced technology. Following this event, Makina declares him her new owner and insists on moving in with him to maintain her cover and receive ongoing maintenance.

In the story, Eita's primary role is that of a reluctant caretaker and live-in mechanic for Makina. Their cohabitation must remain a top-secret arrangement to prevent anyone from discovering her true identity as a robot. This situation places him in constant conflict, as Makina was designed for infiltration and seduction, and she persistently attempts to seduce him. However, Eita is extremely uncomfortable with anything lewd or sexual; he is a pure-hearted virgin who is awkward with women, and his primary interest in her is often framed as a desire to study her intricate design and functions rather than to engage in a physical relationship. This dynamic creates a chaotic romantic comedy where he must navigate her bold but clumsy advances while also helping her hide her robotic nature from the other students.

Key relationships define his interactions throughout the series. His closest friend is Mamimi, who is initially unaware of Makina’s true identity. Eita and Makina arrange to meet Mamimi in a park to receive a hand-me-down school uniform for Makina, but his anxious behavior, stemming from fear of Makina’s malfunctioning leg, leads Mamimi to mistakenly believe he is a dangerous stalker obsessed with the school idol. This misunderstanding becomes a recurring hurdle for Eita as he tries to protect his secret. Another pivotal relationship forms with Mimika, another robot who claims to be Makina’s younger sister. During a confrontation where Mimika steals Makina’s body, Eita reveals his soft-hearted nature by stopping Makina from destroying her opponent. Moved by Mimika’s cunning act of feigned helplessness, he ultimately agrees to let her live with them, much to Makina's jealousy.

Throughout the narrative, Eita undergoes a subtle development primarily driven by his forced closeness with the androids. While he starts as a completely isolated and timid individual, his circumstances push him into a protective role. He demonstrates a willingness to devise strategies to solve problems, such as proposing an otaku-style plan to track down the missing Mimika. He also shows a capacity for courage, rushing to stop Makina from using lethal force against her sister, indicating that his compassion extends beyond machines to all beings, mechanical or otherwise. His mechanical skill is his most notable ability, as he is portrayed as being capable of repairing and maintaining highly advanced androids that are far beyond normal human technology. He is frequently shown performing maintenance, particularly on Makina’s fragile left leg, which is a persistent source of worry for him.