Mayumi is Takakage's childhood friend who has long harbored unrequited feelings for him. Initially attempting to conceal her emotions, she eventually adopts the false identity of "Chisato" to approach Takakage anew. In this persona, she presents herself as an innocent schoolgirl and initiates a romantic encounter with him in a hotel. Overcome by guilt afterwards, she reveals her true identity as Mayumi and confesses her longstanding affection. Takakage rejects her romantic advances, explaining he does not view her in that way.

Earlier, Mayumi demonstrates an interest in fortune-telling. She predicts Takakage will meet and fall deeply in love with a beautiful woman. This prophecy foreshadows his encounter with Ayame, who resembles a figure from his recurring dreams about a past life in Japan's Sengoku era, establishing Mayumi's role in connecting his present to these historical visions.

Her actions throughout the story, driven solely by her unrequited love, lead her into significant personal deception and emotional vulnerability. Takakage's definitive rejection concludes her attempts at romantic involvement with him.