Lucy MacMillan, a young Caucasian researcher and operator for the United Nations Spacy military, serves on the Super Nova project team at the New Edwards Test Flight Center on the colony planet Eden. Her duties focus on supporting the development of the experimental YF-19 variable fighter and monitoring its test flights. With long blond hair and freckles, Lucy becomes romantically involved with the YF-19's test pilot, Isamu Alva Dyson, soon after his assignment. Their relationship features motorcycle rides and intimate moments, including an encounter in bed interrupted by Sharon Apple's fire warning call. During a nighttime pier outing, Lucy's curiosity about flight leads Isamu to demonstrate by running along the pier while mimicking aircraft movements.

At Sharon Apple's Atlantis Dome concert, Lucy attends with Isamu and YF-19 designer Yang Neumann. She reacts visibly to Yang's unauthorized hacking of Sharon's systems, attracting security attention. Lucy's romance with Isamu is complicated by his unresolved past with childhood friends Guld Goa Bowman and Myung Fang Lone.

In the Movie Edition, Lucy's relationship with Isamu follows an alternate trajectory. After the concert, she witnesses Myung intervening in a physical altercation between Isamu and Guld. Later, Lucy informs Myung that Isamu knew about Myung's role in providing emotions for Sharon Apple. Lucy MacMillan appears exclusively in the original OVA and Movie Edition of the Macross series.