Erika Amano is a seventeen-year-old female protagonist with a striking appearance, characterized by long blonde or reddish-blonde hair often styled in pigtails and large purple eyes. Born on April 6, she stands 160 centimeters tall and has AB blood type. Her public image is that of a glamorous and popular social media influencer, with a sizable following that makes her selfies a frequent topic of discussion. Despite this online fame, her life is complicated by a secret that was revealed only recently: she was switched at birth with Nagi Umino, a boy her age from a modest family, and was raised as the heiress to the wealthy Amano family, which owns a major hotel chain.

At the start of the story, Erika lives in a state of privilege but also feels trapped, as her adoptive parents have arranged for her to marry the son of her biological parents to resolve the decades-old hospital mix-up. Initially unaware of the full truth, she meets Nagi by chance and asks him to pose as her fake boyfriend in a desperate attempt to avoid an unwanted engagement. The irony of the situation becomes clear when they both discover that he is the very person her parents have chosen for her, a twist that throws her into confusion and forces the two to begin living together.

Personality-wise, Erika is a complex character who often appears as a bright, energetic, and spirited young woman. However, she also exhibits a tsundere nature, frequently hiding her true feelings behind a proud or brash exterior. She is used to a life of luxury and can come across as spoiled or vain, but she actively avoids the negative extremes of a selfish "himedere" archetype. Beneath her confident facade, she is surprisingly awkward in social situations and struggles to make friends, feeling isolated by her status. Her sheltered upbringing has also left her inexperienced with ordinary daily tasks, leading to clumsy moments and a childlike wonder for simple things like instant noodles. At her core, she is a caring and compassionate person, eager to support the people she comes to care about.

Erika's key relationships drive much of her personal development. Her relationship with Nagi Umino begins as a reluctant engagement and a matter of convenience, but through forced cohabitation, they develop a mutual respect and bond, with her eventually falling in love with him. She shares a particularly affectionate bond with Sachi Umino, her biological younger sister, and prioritizes making her happy. At school, she befriends Hiro Segawa, who is initially a fan of her social media presence and helps her acclimate to a new academic environment. Her dynamic with her adoptive parents is supportive, even as she navigates her feelings about her biological parents, Yohei and Namie Umino.

Regarding her abilities, Erika possesses natural athletic talent and is notably good at sports. She also has a talent for leveraging her beauty and personality as a social media influencer, though this fame is a double-edged sword that has, at times, led to controversies and her needing to transfer schools. Academically, she is initially behind her peers at the more rigorous Megurogawa Academy, requiring her to apply herself diligently in study sessions to catch up. Her hobbies include cosplay, photography, and she has quirky interests such as a love for dinosaurs and a specific preference for thin-crust pizza. Throughout the narrative, Erika grows from a somewhat carefree and sheltered girl into a more self-aware individual who actively works to understand her own identity and build genuine connections with both her new family and her fiancé.