Erika is a secondary character in the anime, recognized as a classmate of the main protagonists Yuki Sanada, Haru, Natsuki Usami, and Akira Agarkar Yamada. She is seated next to Yuki in their classroom, placing her in a familiar position relative to the central group. Her full name is Erika Usami, indicating her connection to a notable family on the island of Enoshima. She is the granddaughter of the town's mayor, a detail that is revealed later in the series and links her to the local leadership and the temple where the mayor also serves.

In terms of personality, Erika is depicted as a proactive and spirited individual, particularly within the school setting. She takes initiative and is comfortable organizing group activities, as seen when she takes charge of her class project for the school festival. She efficiently delegates tasks, assigning the main characters to build a fish pond for their curry stall and confidently rallying the class around the plan. Her demeanor is friendly and encouraging, often expressing confidence in the abilities of her classmates, such as when she refers to Yuki, Haru, and Natsuki as fishing experts. Her motivation is largely tied to her social environment and school life, focusing on successful collaboration with her peers.

Within the story, Erika primarily serves as a supporting character who helps ground the narrative in the everyday setting of high school, contrasting with the more fantastical elements of alien invasions and mysterious fishing techniques. Her role is to be a familiar face and a point of connection for the main characters within their community. She is instrumental in facilitating the school festival event, which brings the main group together for a common goal. Her relationship with the main characters is that of a reliable and friendly peer. She interacts with Yuki, Haru, Natsuki, and Akira as classmates, showing no visible awareness of their more extraordinary secrets, such as Haru's alien nature. Her connection to Natsuki is likely through shared family ties, as they are both members of the Usami family, though the specific nature of their relation is not explicitly detailed.

As a supporting character, Erika does not undergo a significant personal development arc. Her presence and role remain consistent as an affable and capable class representative figure. The narrative does not depict her with any notable supernatural abilities or specialized skills, instead portraying her as a regular high school student who is adept at social coordination and school activities. Her heritage as the mayor's granddaughter is a notable aspect of her background, but it does not grant her any special powers or responsibilities that directly impact the main plot involving the Bermuda Syndrome or the alien characters.