Nae Kogure is a young woman who appears in the story arc of Mermaid Forest, encountered by the immortal protagonist Yuta in the years before World War II. She is depicted as a beautiful teenage girl with long black hair and dark eyes. Nae became intrigued by Yuta and eventually learned of his curse of immortality, which led her to share a secret of her own: she had once obtained ashes from a mermaid and spread them across a hillside of red flowers, causing them to bloom eternally, never wilting regardless of the season. This place, known as Red Valley, became a private meeting spot for the two. Despite being engaged to a man named Eijiro, Nae and Yuta fell deeply in love and began a secret romance, meeting regularly in the valley sustained by the mermaid's ashes. Nae's motivations are rooted in a genuine emotional connection with Yuta rather than a desire for immortality itself. She demonstrates a trusting and affectionate nature, willing to keep Yuta's secret and risk societal disapproval for the bond they share. In the overall narrative, Nae serves as a poignant figure from Yuta's past, illustrating the loneliness and longing for connection that defines his centuries-long existence. Her relationship with him represents one of the few times he allowed himself to form a close human attachment. Her development is tied to the passage of time and the inevitable separation that comes with Yuta's immortality. While she has no supernatural abilities herself, her knowledge of the mermaid's ashes and her willingness to share that knowledge with Yuta are notable, as the ashes' perpetual blooming stands as a symbol of her love and sacrifice. Her story ultimately underscores the tragedy of mortal ties in an immortal life.