Erika Kouenji is a minor antagonist from the commercial audition arc, serving as an old rival to Kanae Kotonami. She is the daughter of the head of the wealthy and powerful Koenji Group, and she leverages this immense family fortune to pursue her dream of becoming a star. Physically, Erika is depicted with straight dirty blonde hair and brown eyes, and she typically dresses in elegant clothes that reflect her privileged upbringing.

Erika is defined by an arrogant, conceited, and deeply spoiled personality. She is extremely competitive, believing that her family's money can and should buy her anything she wants, including success in the entertainment industry. Her typical approach to auditions involves flaunting her wealth and connections, and she has been known to attempt to bribe directors and producers to secure roles. Despite her reliance on underhanded tactics, she is genuinely confident in her own talents, which include professionally trained classical ballet. Erika expects everyone to defer to her whims, and she becomes enraged when she does not get her way, showing a complete inability to accept defeat gracefully.

Erika's central role in the story is defined by her antagonistic relationship with Kanae Kotonami, whom she considers her rival. This fixation began when they were in the third grade, both competing for the lead role in a school play. Kanae won the part through a public vote by their classmates, and Erika, consumed by jealousy, has spent years trying to sabotage Kanae's path to becoming an actress. She is single-minded in her harassment, using her family's influence to block Kanae from joining the drama club in middle school and even ordering her employees to break into the school to discover which high school Kanae would attend.

Her role in the main narrative culminates during an audition for a commercial. There, she confronts Kanae and Kanae's Love-Me Section partner, Kyoko Mogami. Dismissing Kyoko as a talentless poor person, Erika focuses her ire on Kanae, whom she insults and attempts to intimidate. When the commercial's director, Ushio Kurosaki, resists her bribes, Erika resorts to other dishonest means, including spying on Kyoko to steal her improvisation idea for the audition. After losing the role to Kanae and Kyoko, Erika's vendetta escalates as she orders her bodyguards to physically attack Kanae in an attempt to injure her face so she cannot film the commercial.

Erika is almost always attended by three servant-bodyguards whom fans have nicknamed the Jewel Squad, as each is named after a gemstone: Emerald, Sapphire, and Ruby. These followers are as amoral as their mistress, eagerly complying with her every demand, no matter how illegal or cruel. While she shows little respect or interest in anyone else, the director Kurosaki recognizes that despite her reliance on money, Erika does possess a measure of genuine acting ability.

Over the course of this arc, Erika experiences a small degree of forced development. After her direct confrontation with Kanae, who declares she will never accept her as a rival until she stops using her family's wealth and strives on her own merits, Erika appears to reconsider her tactics. This leads her to decide to stop relying on the Koenji name to secure roles and to focus on her own skills instead. Beyond her known talent for ballet and her ability to copy other actors' ideas, Erika has no other significant or notable abilities as an actress that are not bolstered by her wealth.