For twelve years, Mifu Miyabi believed she was completely alone in the world, growing up without parents or siblings. That belief shatters when three identical girls who look exactly like her suddenly appear, revealing that she is actually a quadruplet. Though they share the same face, each sister has grown up in a completely different environment, and their personalities are far more distinct than their appearance suggests.

The story follows Mifu and her three newly discovered sisters as they move in together and attempt to navigate life under one roof. Set in contemporary Japan, the light novel explores the challenges and joys of forming familial bonds from scratch, as girls who are strangers to one another must learn to coexist, share a living space, and build sisterly relationships. The series emphasizes themes of family, sisterhood, and the discovery that being identical in looks does not mean being identical in heart.

As the quadruplets adjust to their new living arrangement, each volume chronicles their daily adventures, misunderstandings, and moments of genuine connection. The central conflict revolves not around external threats but the internal challenge of transforming four separate individuals into a cohesive family unit. Notable narrative arcs include the initial shock of discovery, the awkward early days of cohabitation, learning to distinguish one another beyond physical appearance, and gradually uncovering the circumstances that led to their separation at birth. The series maintains a focus on middle-grade audiences, capturing both the comedic mishaps and heartfelt milestones that come with gaining three sisters overnight. With the first English volume subtitled The Start of Our Secret Life as Sisters, the story establishes its core premise of four identical girls embarking on an unprecedented journey to become a family.