A socially isolated and self-dramatizing middle school student, Kyotaro Ichikawa, harbors dark fantasies of murdering his popular classmates, frequently reading a murder encyclopedia and picturing violent scenarios. His primary imagined target is Anna Yamada, the tall, beautiful, and admired class idol who also works as a magazine model. The setting is Daijuni Middle School, where Kyotaro spends much of his time alone in the school library, the same place where Anna secretly indulges her biggest weakness: a massive appetite for snacks and candy, which are prohibited on school grounds.

The central conflict and story begin when Kyotaro starts observing Anna in the library. Instead of finding a cold, untouchable idol, he discovers she is quirky, clumsy, and odd in her own endearing ways. Despite his murderous delusions, he finds himself impulsively helping her, whether by lending a box cutter, creating a distraction to ward off an annoying upperclassman, or covering for her when she gets in trouble. These actions confuse Kyotaro, as they contradict his self-image as a dangerous loner. Through a series of daily encounters, his violent fantasies are slowly replaced by genuine romantic affection, though his crippling low self-esteem and lack of social skills make it difficult for him to understand or express his true feelings.

The first major narrative arc focuses on the awkward and tender development of their friendship. Kyotaro begins to see past Anna's popularity to her genuine, kind, and sometimes anxious personality. Anna, in turn, shows a persistent interest in Kyotaro, appreciating his perceptiveness and the way he treats her like a normal person rather than an idol. Key events include their interactions during a school festival, a workplace experience trip, and various holidays. The season culminates in Kyotaro finally acknowledging his love for her and wanting to become someone worthy of her affection.

The second season deepens their relationship as they enter a new school year. Kyotaro struggles with his growing feelings and the desire to bridge the gap between their different social worlds. Notable arcs include navigating the complexities of Valentine's Day and White Day, a trip to Anna's family home where Kyotaro meets her parents, and a school sports festival that becomes the stage for a public, albeit indirect, confession of his feelings. The series builds towards a heartfelt conclusion where both characters confront their emotions, leading to a mutual confession in the library, the place where their entire relationship began. Throughout both seasons, the side cast, including Anna's close friends and Kyotaro's classmates, provide support, comic relief, and sometimes unintentional obstacles, all while the two protagonists slowly grow from distant classmates to a genuine couple.