Kyosuke Date, a young man, awakens in a hospital after a violent attack that leaves his sister, Runa, in a coma. The incident is tied to a mysterious organization known as the Hospital, which conducts unethical experiments on humans to create beings called Soultakers. These experiments involve extracting souls to create powerful entities, and Kyosuke discovers he is no ordinary human—he possesses a dual nature, with a monstrous alter ego called the Soultaker. This transformation grants him immense power but comes at a cost, as it threatens to consume his humanity.

Kyosuke’s journey revolves around uncovering the truth behind the Hospital and its leader, Dr. Mamiya, who has a personal connection to his past. Along the way, he encounters a diverse cast of characters, each with their own motivations and ties to the Hospital. Among them is Komugi Nakahara, a cheerful and resourceful girl who becomes Kyosuke’s ally, and Shiro Mibu, a stoic and enigmatic figure who wields a sword and harbors secrets of his own. The narrative also introduces the enigmatic Kirihara siblings, who play a pivotal role in the unfolding events.

As Kyosuke delves deeper into the Hospital’s operations, he learns of the Soultaker Project, an initiative aimed at creating perfect beings by merging human souls with artificial constructs. The project’s ultimate goal is to transcend human limitations, but it comes at the expense of countless lives. Kyosuke’s quest intertwines with themes of identity, morality, and the consequences of tampering with the soul. The story builds toward a climactic confrontation with Dr. Mamiya, whose ambitions threaten to unravel the fabric of reality itself.

The series blends elements of science fiction, horror, and psychological drama, with a narrative structure that incorporates flashbacks and nonlinear storytelling to reveal the characters’ backstories and motivations. The interplay between Kyosuke’s human and monstrous sides serves as a central conflict, exploring the duality of his existence and the struggle to retain his humanity in the face of overwhelming power. The plot is driven by a mix of action, mystery, and philosophical undertones, culminating in a resolution that ties together the fates of the characters and the consequences of their choices.