Eiko Tsukimi is the central musical protagonist of the story, a young and ambitious singer-songwriter whose journey from obscurity toward stardom forms the emotional core of the film. With long, light blonde or yellow hair typically styled in two ponytails and blue eyes, she has a distinct and memorable appearance that often includes casual clothing such as hoodies, caps, and shorts. Her age is approximately twenty-one, and she has a background marked by significant personal hardship.

Born in Kyoto, Eiko was raised in a complicated family environment where her love for music, nurtured by her musician father, clashed with her mother's practical disapproval. The sudden disappearance of her father during her childhood was a traumatic event that left deep emotional scars. During a high school trip to Tokyo, her despair reached a breaking point, leading her to attempt suicide at Shibuya Station. She was rescued by Kobayashi, the owner of the live music venue BB Lounge, who offered her a second chance. That same night, a performance by an American singer inspired her to pursue singing as a reason to live, leading her to move to Tokyo and work at his lounge.

Eiko's personality is defined by a quiet, humble, and introspective nature, frequently shadowed by low self-esteem and self-doubt. She constantly questions whether she has the talent to succeed in the competitive music industry, despite possessing a voice that anyone who hears it finds captivating. This internal conflict between her profound passion for music and her deep-seated insecurity is a central aspect of her character. She is also kind and sincere, a trait that allows her to form genuine connections even with rivals, though she can be perplexed by the esoteric historical references made by her manager, the ancient strategist Kongming.

In the film, Eiko continues to be guided by Zhuge Kongming, the legendary tactician from China's Three Kingdoms period who now serves as her manager. While she initially accepted his help in a state of desperation, she has grown to trust him implicitly, proudly introducing him as her soldier. Their relationship is a unique partnership where Kongming devises strategic plans to promote her career, believing that his role is simply to create opportunities for her genuine talent to be heard. Eiko's primary motivation is to share her song and connect with people's hearts through her music, a pure desire that Kongming recognizes as a form of bringing peace to the people in the modern world. The film explores Eiko's struggle with self-confidence as she faces new, high-stakes challenges, pushing her to find her authentic voice both as an artist and as a person.

Her key relationships are essential to her development. Kobayashi, her employer and savior, acts as a benevolent father figure and guardian, providing her with a stable environment to grow. She also has a complex relationship with Nanami Kuon, a fellow performer who evolves from a rival into a source of mutual artistic respect and personal inspiration. These interactions push Eiko to confront her own artistic identity and her reasons for singing.

Eiko's most notable ability is her singing voice, which is portrayed as exceptionally pure and emotionally resonant, capable of moving listeners on a profound level. She is a talented songwriter and guitarist, writing and composing her own material. While her technical skill is high, her true power lies in the emotional authenticity of her performances, which can inspire others and, as depicted in the film, even stir the memories and spirits of those from the past. Her development throughout the story is a process of learning to believe in this inherent ability, transforming from a struggling, uncertain amateur into a confident performer capable of carrying her own dreams forward.