Tsubomi Tachibana is a fifth-grade student confronting the challenges of early adolescence. Significant personal milestones shape her experience, including her mother's pregnancy, delighting her with the prospect of a sibling while also sparking confusion about adult relationships and conception.

She faces physical changes like her first menstruation, initially attempting to handle it alone due to embarrassment, reflecting her tendency to internalize struggles despite being generally responsible and helpful. Naivety surfaces in her misunderstandings about bodily developments and interpersonal dynamics.

Emotionally, confusing feelings develop around classmate Daiki Nemoto, causing her to blush in his presence without recognizing them as romantic attraction. Daiki comforts her during stressful times, such as visiting her mother in the hospital, and gives her a toy duck that becomes a cherished keepsake on her bag. Witnessing friends kiss clarifies their mutual feelings; Tsubomi eventually confesses to Daiki, and they become a couple.

Her friendships are central. She relies on best friends Yae Yamabuki and Rea Katō for support, while new transfer student Saya Endō acts as an older-sister figure, offering guidance on personal issues. Tsubomi occasionally feels jealousy when Saya interacts with Daiki, revealing her evolving emotional complexity.

Across her journey, she moves from confusion to gradual self-awareness regarding physical maturation, romantic emotions, and family changes.