Shizuka reconnects with her childhood friend Kousuke Atami after years apart, holding fast to a shared childhood promise she interprets as a serious romantic commitment. Now a high school student, she discovers Kousuke has become a socially marginalized and overtly perverted individual, starkly contrasting her own evolution into a more assertive personality. This difference immediately strains their renewed interactions at school.

Despite Kousuke's frequent sexual encounters with other female classmates—his method for solving their personal problems—Shizuka consistently demonstrates genuine affection towards him. Her emotional investment persists despite these distractions. Gradually, through navigating these complexities and shared experiences, their bond deepens, moving them toward a closer connection and evolving mutual understanding.

Shizuka transformed from a sweet-natured child into this determined young woman, her loyalty and earnest approach to relationships underscored by her commitment to the childhood promise. Her physical appearance features a distinctive hairstyle that changes after the first episode, becoming consistent thereafter.

Involved closely in Kousuke's life, she often witnesses or is indirectly affected by his escapades with other women. Yet, her persistent emotional attachment drives her to consistently engage with him, centering her involvement around their connection and the school environment.