Akihito Aoyagi is a high school student whose quiet, routine life is disrupted by the arrival of Charlotte Bennett, an elegant and beautiful exchange student from England. While Charlotte quickly becomes popular with everyone in class, Akihito keeps his distance, feeling that someone like her belongs to a completely different world. His perspective changes when he helps a lost little girl, only to discover that the child is Charlottes younger sister, Emma, and that the two sisters have just moved into the apartment next door.

Following this incident, young Emma grows strongly attached to Akihito, and soon both sisters begin visiting his room regularly. What develops is an unconventional domestic relationship where the trio spends time together through simple everyday activities such as sharing meals, playing games, and going on outings. Through these shared experiences, the initial awkwardness between Akihito and Charlotte gradually fades as they grow closer, with Emma often acting as an innocent catalyst that brings the two older characters together. The story explores their journey from being neighbors with a secret connection to navigating the complexities of becoming a couple while managing the reactions of those around them.

The main characters include Akihito Aoyagi, a student who carries burdens from a difficult past in middle school that continues to affect his present relationships; Charlotte Bennett, the elegant exchange student who becomes more affectionate and proactive as her feelings develop; and her younger sister Emma, an energetic and sweet-natured child whose attachment to Akihito is a primary driver of the storys events. Secondary characters include classmates like Shimizu Arisa and Shinonome Karin, who participate in social events such as Charlotte's welcome party, as well as a junior named Kosaka Kaede who reappears from Akihito's troubled middle school days.

The narrative spans several arcs that develop the central relationship. The initial arc establishes how Akihito helping Emma breaks down the distance between him and Charlotte, leading to the sisters becoming regular visitors to his apartment. A subsequent arc focuses on episodes like celebrating Emmas first day at preschool and resolving sibling conflicts between Charlotte and Emma, during which Akihito becomes more deeply integrated into their family dynamic. Another significant arc follows Charlotte and Akihito as they officially become a couple, leading to a dramatic shift as their relationship becomes known at school and provokes strong reactions from classmates who idolize Charlotte and view Akihito negatively. This arc forces Akihito to confront his traumatic middle school past directly, particularly through an upcoming sports tournament where he must prove himself. Additional storylines include Emmas birthday celebration, Charlotte becoming interested in new experiences like playing video games, and the ongoing challenge of whether the pair can keep their relationship discreet at school while growing increasingly affectionate in private.