"Baby Baachan" centers around an elderly woman who mysteriously reverts to the physical appearance of a baby while retaining her adult mind and memories. The sudden transformation occurs without explanation, leaving her family and community baffled. Despite her infantile appearance, she continues to navigate her daily life with the wisdom and experience of her years, often leading to humorous and heartwarming situations as she interacts with her family, neighbors, and the world around her.

The protagonist, referred to as Baachan (a term of endearment for "grandmother"), lives with her son, daughter-in-law, and young grandson. Her family struggles to adjust to her new form, balancing their respect for her as the matriarch with the challenges of caring for someone who looks like a baby. Baachan’s sharp wit and no-nonsense attitude often clash with the limitations of her tiny body, creating a dynamic interplay between her inner maturity and outward appearance.

As the story progresses, Baachan’s transformation becomes a catalyst for exploring themes of aging, family dynamics, and societal perceptions of the elderly. Her interactions with her grandson, in particular, highlight the generational gap and the mutual learning that occurs between them. Despite her predicament, Baachan remains a pillar of strength for her family, offering guidance and support while adapting to her new reality.

The series also delves into the reactions of the broader community, ranging from curiosity to skepticism, as Baachan’s situation becomes public knowledge. Her resilience and determination to live life on her own terms inspire those around her, even as she grapples with the practical challenges of her condition. The narrative balances lighthearted moments with poignant reflections on life, identity, and the passage of time, making "Baby Baachan" a unique blend of comedy and drama.