Koharu Koga is a twelve-year-old idol trainee defined by a sweet, gentle, and calm disposition, consistently appearing with a cheerful smile and a soothing presence that comforts those around her. She is deeply thoughtful and considerate toward her fellow unit members. Her primary motivation is a long-held dream of becoming a princess, which she expresses through a love of fairy tales and a creative hobby of sketching cute, frilly stage costumes. She takes great joy in caring for her pet iguana, Hyou-kun.

Within the narrative, Koharu acts as a warm and stabilizing core member of her idol group. She participates fully in the unit's training and public performances and is a member of a marching band sub-unit where she plays hand bells. Her key relationships include studying and spending time with Arisu Tachibana and Mary Cochran, and sharing an energetic rapport with Miria Akagi during marching activities. Over the course of her development, she works on overcoming slight clumsiness in dance and a tendency to wander off, gradually building confidence in her performance abilities and learning to translate her gentle nature into an engaging stage presence. Her notable traits include a natural talent for offering sincere compliments and a distinct creative vision for idol fashion design.