"Kanban Musume wa Sashiosae" centers on the life of Sashio, a high school girl who works part-time at her family's traditional Japanese confectionery shop. The shop, known for its long-standing reputation, faces financial difficulties due to changing consumer preferences and competition from modern dessert establishments. Sashio, determined to save the family business, takes it upon herself to innovate and attract new customers while preserving the shop's traditional charm.

The narrative explores Sashio's efforts to balance her school life with her responsibilities at the shop. She experiments with new recipes, incorporates modern marketing strategies, and collaborates with her classmates to create unique confections that appeal to younger generations. Along the way, she encounters challenges such as skeptical customers, rival businesses, and the pressure to maintain the shop's legacy. Despite these obstacles, Sashio's creativity and perseverance drive the story forward.

Key characters include Sashio's supportive but traditional-minded parents, who initially resist her modern ideas but gradually come to appreciate her efforts. Her classmates, particularly a close friend who assists her in brainstorming and promoting the shop, play a significant role in the story. The series also features recurring customers and local business owners who provide both encouragement and competition, adding depth to the community-centered setting.

The plot is structured around episodic challenges, with each chapter focusing on a specific problem or opportunity for the shop. Themes of tradition versus innovation, family legacy, and the importance of community are woven throughout the narrative. The story maintains a lighthearted tone, with moments of humor and heartfelt interactions, while also addressing the realities of running a small business in a rapidly changing world.