The narrative begins on a full moon night, where the protagonist, Isaka Kouta, a seventeen-year-old high school student, casually remarks, "The moon is beautiful." This simple observation elicits a surprised reaction from his classmate, Ayashiro Shiori, who walks beside him. Shiori, a popular, beautiful, and athletic girl, is taken aback by his directness, implying she had a similar thought but was too shy to voice it. This seemingly minor exchange marks the beginning of a shift in Kouta's environment.
Kouta is a relatively ordinary student, contrasting with Shiori's exceptional popularity. His classmate, Shiba Ri Anna, a lively girl who often relies on Kouta for notes, points out his unusual closeness with Shiori, despite them rarely interacting in class. Kouta explains they share a middle school background and often walk home together, leading to more in-depth conversations than their classroom interactions suggest. He values his peaceful, ordinary life, which includes his friendships.
Shiori approaches Kouta during a break, asking to speak privately. She expresses concern about his interactions with Anna, particularly their note-sharing and Anna's overly familiar "I love you." Shiori feels their closeness is inappropriate, especially when she overhears such declarations. Kouta, initially confused, agrees to be more mindful. Shiori then expresses a desire to be called by her first name, "Shiori," instead of her surname, "Ayashiro," which Kouta finds difficult due to her imposing aura. He agrees to consider it, but the conversation leaves him feeling unsettled, hinting at a deeper misunderstanding or a potential for a relationship beyond friendship.
The next day, Kouta's badminton club practice ends early. He encounters Shiori outside the gym, who claims she waited for him. This is unusual as their club schedules often differ. She insists on walking home together, and during their walk, she reiterates her desire to be called "Shiori," which Kouta reluctantly agrees to for future interactions.
The following morning, the classroom is abuzz with gossip: Shiori has a boyfriend. Anna reveals that Shiori accidentally let slip this information, causing a stir. Kouta is shocked, as Shiori has never been in a relationship despite her popularity. He speculates it might be a misunderstanding or a close friend. When he questions Shiori, she tearfully confesses that she believed he confessed his feelings to her two days prior, during their walk home. Kouta, having no memory of this, is thrown into confusion. The class, witnessing Shiori's distress, turns against Kouta, accusing him of being cruel.
To de-escalate the situation and avoid further backlash, Kouta, despite his confusion, decides to go along with the narrative. He apologizes for his initial denial, claiming he was unsure if his "confession" was understood and hesitated to confirm their relationship publicly. He then asks Shiori to be his girlfriend, which she happily accepts. Their newfound relationship is met with a mix of congratulations and warnings from their classmates. Kouta plans to discuss the situation further with Shiori later.
Later, Kouta's badminton clubmate, Honomura Chisaki, confronts him about the rumors. She expresses concern, reminding him of his past heartbreak from a cheating ex-girlfriend and his vow to avoid romance. Kouta confirms his relationship with Shiori but avoids giving details, leaving Chisaki visibly upset and concerned. Kouta reflects on his past relationship, where his girlfriend's infidelity led to their breakup and his subsequent reluctance to trust and engage in romantic relationships. He realizes his past trauma makes him hesitant to fully embrace his new relationship with Shiori, despite her apparent affection.