Eiko Shimao is introduced as the reigning lead actress at Ginei Studios, a major film production company, at the time when the much younger Chiyoko Fujiwara begins her acting career. Physically, she is depicted as an adult woman with black eyes and black hair cut to neck length.

Her personality, as revealed through her interactions with others, is marked by a sharp condescension and a sense of superiority. Upon first meeting the new young actress, she deliberately mispronounces Chiyoko's name, calling her Chieko, and continues to incorrectly address her, later saying So, your name is Chizuko. This behavior signals her disdain and dismissive attitude toward a potential rival. She also demonstrates a cynical worldview, contrasting sharply with Chiyoko's earnest romanticism. During a scene where both are dressed as prisoners, Eiko mocks Chiyoko's steadfast loyalty, arguing that feelings change over time, a direct challenge to Chiyoko's declaration of eternal love for the man she is seeking. Her dialogue in another film scene reveals a cruel practicality, telling a character who wants to give a final gift to a condemned man that a man about to be executed does not need anything.

Initially, Eiko pretends to be helpful towards Chiyoko, even taking her to a fortune teller who sends the younger actress on a long, fruitless journey to the north of Manchuria. This act, however, is later revealed to have been a calculated deception born from professional jealousy. It is disclosed that Eiko was jealous of Chiyokos rising talent and stole the precious key Chiyoko had received from the mysterious artist she had been trying to find for years. Eiko not only stole the key but also paid the fortune teller to mislead Chiyoko, all in an effort to send her away and potentially derail her career. She later gave the stolen key to Junichi Ootaki, the director's son who would go on to marry Chiyoko. Her confession of this act comes years later when Chiyoko finds the key hidden in her home and confronts her husband, exposing Eiko as the architect of a decades-long deception.

Eiko's role in the narrative is primarily that of an antagonist within the film studio. She represents the professional rivalry and personal jealousy that Chiyoko faces in her quest for the mysterious painter. Her character illustrates the more pragmatic and self-serving motivations that can exist in the world of show business, contrasted with Chiyokos pure and lifelong devotion to a single, seemingly hopeless goal. Eikos actions directly shape the course of Chiyokos life, causing her to abandon her search for a time and enter a marriage. She does not undergo a significant personal transformation within the story; instead her development is one of revelation, moving from a seemingly friendly senior colleague to a confessed saboteur whose envy had a profound and disruptive impact on the protagonists life journey. Her defeat is not a dramatic downfall but a quiet confession that reveals the hidden obstacles Chiyoko unknowingly overcame.