Erika Campbell is a main character known for her distinctive appearance, which sets her apart within her social circle. She is tall, has dark skin, and possesses white hair. At seventeen years old with a birthday on January 27, her unique look is a direct result of her mixed heritage, as she is half-Brazilian from her father's side and half-Japanese from her mother's side. She came to live in Japan from Brazil alongside her adopted brother, Takumi, who later became a famous rock star in the band Third Sence.

Erika's background as a foreigner in Japan is central to her character, as she was constantly picked on by her peers for not knowing anything about Japanese culture. This feeling of alienation is what encouraged her to answer the casting call for the Lemon Angel project, as she longed to become part of a group where she could belong. Her personality is notably bright and cheerful, making her the mood-maker within the group. She is a fiercely loyal and proactive friend; she was the first to befriend Tomo and forcefully tried to help Saya even when Saya repeatedly rejected her assistance. She consistently sticks up for Tomo and Saya, and her primary desire is for everyone to stop fighting and become friends.

Her key relationships are the cornerstone of her role in the story. Her bond with her adopted brother Takumi is exceptionally strong, as she feels a deep need to protect him. Her friendships with Tomo and Saya are equally vital; she considers them her closest friends, and their mutual support forms a core part of the narrative. Erika is also noted for having practical skills, including being a great cook and being skilled at sewing.

Erika undergoes significant development during a major plot point where a tabloid reporter discovers the secret that she and Takumi are not blood relatives and threatens to expose them as a couple living together. The reporter manipulates the situation, making Erika feel she must leave the group to protect her brother, who she believes is unaware of their true relationship. Believing the scandal will ruin the Lemon Angels, she runs away. However, Tomo and Saya refuse to abandon her, chasing after her and affirming that they are close friends no matter what. This crisis culminates in Takumi revealing that he has always known the truth and considers her his beloved sister, and the scandal is ultimately diffused. This experience demonstrates Erika's initial vulnerability regarding her family secret but ultimately reinforces the strength of her bonds with both her brother and her fellow Lemon Angels, who prove their loyalty to her.