"Twin Dolls" is a psychological thriller anime that explores themes of identity, duality, and the consequences of unchecked ambition. The narrative centers on two genetically engineered sisters, Aya and Yuki, created as part of a clandestine project to develop perfect human beings. Raised in isolation within a high-tech facility, the sisters are trained to excel in combat, intelligence, and adaptability, but their creators impose strict control over their emotions and individuality.

The story begins with the sisters' escape from the facility after a catastrophic event exposes the darker intentions of their creators. Aya, the more assertive and protective sister, takes the lead in navigating the outside world, while Yuki, who is more introspective and emotionally fragile, struggles to reconcile their artificial origins with their growing sense of humanity. As they evade capture, the sisters encounter a diverse cast of characters, including former test subjects, rogue scientists, and shadowy figures tied to the project. These interactions force Aya and Yuki to confront their purpose and the ethical implications of their existence.

The plot unfolds through a series of flashbacks and present-day events, revealing the sisters' shared memories of the facility and the experiments they endured. Key revelations include the existence of other genetically modified individuals, some of whom harbor resentment toward Aya and Yuki for their perceived superiority. The sisters' bond is tested as external threats and internal conflicts escalate, particularly when Yuki begins to question whether their creators' vision of perfection is worth pursuing.

Aya and Yuki's journey is marked by moral dilemmas and moments of self-discovery. Aya's determination to protect her sister often clashes with Yuki's desire for autonomy, creating tension that drives much of the narrative. The series also delves into the motivations of the project's overseers, who view the sisters as tools for advancing their own agendas. As the story progresses, the sisters must decide whether to embrace their engineered nature or forge their own path, free from the constraints of their creators' designs.

The anime balances action-packed sequences with introspective moments, highlighting the sisters' evolving relationship and their struggle to define themselves in a world that sees them as both miracles and abominations. The narrative builds toward a climactic confrontation with the project's leaders, forcing Aya and Yuki to confront the ultimate question of what it means to be human. The series concludes with an open-ended resolution, leaving room for interpretation regarding the sisters' future and the legacy of the project that created them.