Emi Kaido is the central protagonist of her story, a seventeen-year-old high school girl living in the Shibuya district of Tokyo. Her family situation is a primary factor in shaping her distant and detached demeanor; she lives alone in a large apartment because her father left for unexplained reasons when she was young and has been largely absent from her life since. This prolonged isolation has led her to develop a protective shell of cynicism and disaffection. Emi is often described as aloof and listless, holding a "devil-may-care" attitude that sometimes manifests in risky behavior, as if she is daring the world to prove its worth. Beneath this jaded exterior, however, is a profound sense of emptiness and a secret desire for excitement or meaning in her life.

Despite her emotional barriers, Emi possesses notable practical skills and interests. She has a love for tinkering with mechanical objects, taking them apart to understand how they work and often reassembling them better than before. This mechanical inclination naturally developed into a talent for drawing, which is a significant aspect of her character. This particular skill becomes a key part of her role in the narrative when she comes into possession of a mysterious artifact known as the "Case". The Case is a wish-granting device that, in Emi's hands, reflects her heart's desire by taking the form of a large, childish-looking pencil she calls her "Possibility Pencil". When she draws with it, she can materialize the things she sketches, a power she initially uses for simple tasks like summoning a lost lunch before learning its true potential.

As the story progresses, Emi's most significant action with this pencil is to summon four legendary heroes from destroyed parallel worlds to protect her: Ken the Eagle (Gatchaman), Tekkaman, Casshan, and Hurricane Polymar. Her role in the narrative is to be the linchpin that holds these heroes together, serving as both the center of the conflict and the focus of a coming-of-age journey. Initially a reluctant participant, she often needs to be protected, but she eventually grows to stand on her own and provides crucial support to the heroes. Her development forms the emotional backbone of the series, as the heroes help break through her crusty exterior. Each hero interacts with her differently, aiding her growth: Ken offers emotional support and is most persistent in reminding her she is not alone, Casshan helps her understand her relationship with her father through his own tragic backstory, Tekkaman provides logical explanations for the events unfolding, and Hurricane Polymar acts as a link to her contemporary world. Through these relationships, she learns to look beyond her own pain and isolation.

The central crux of Emi's journey is deeply connected to her father, who is eventually revealed to be the primary antagonist, a man known as Z. His original wish, made using the Case, was to protect Emi from what he believed was a destined tragic death that would occur in any parallel world. In his grief and fear, he became a destroyer of other worlds, sealing Emi away in a closed world to keep her safe, which manifested as a small sun based on a memory of a sunset they shared. Emi's final challenge is to save her father's heart. Using her determination and the memory of everything she learned from the heroes, she reaches out to him during the final battle, reminding him of their precious memory by the beach. This act breaks through his armor of grief, allowing him to see that she has grown up and can choose her own possibilities. Emi's notable ability, beyond her mechanical and artistic talents, is therefore her willpower and emotional growth; her power with the Case is intrinsically linked to her state of mind and her desire to forge her own path, ultimately using the pencil not just to summon heroes but to help save the man her father used to be.