"Chained Soldier" is set in a world where humanity faces an existential threat from mysterious creatures known as Shuuki, which emerge from portals called Mato. These portals appear randomly across the world, unleashing monsters that wreak havoc. To combat this threat, an elite force of soldiers, primarily women known as the Peach Corps, is formed. These soldiers wield unique powers granted by special fruits found within Mato, which enhance their abilities and allow them to fight the Shuuki effectively.

The protagonist, Yuuki Wakura, is an ordinary young man who becomes entangled in this conflict after a chance encounter with a member of the Peach Corps, Kyouka Uzen. Kyouka, a high-ranking officer, discovers that Yuuki possesses a rare ability to form a symbiotic bond with her, amplifying her powers significantly. This bond, referred to as a "chain," allows them to fight together as a formidable team. However, the bond also comes with a unique condition: Yuuki must submit to Kyouka’s authority, creating a dynamic of control and dependence between them.

As the story progresses, Yuuki and Kyouka are joined by other members of the Peach Corps, each with their own distinct abilities and personalities. The group works together to protect humanity from the Shuuki while uncovering the mysteries of Mato and the origins of the fruits that grant their powers. The narrative explores themes of power dynamics, loyalty, and the moral complexities of using supernatural abilities in warfare.

The plot delves into the political and social structures within the Peach Corps, revealing internal conflicts and rivalries among its members. The series also examines the psychological toll of constant battle on the soldiers, as well as the ethical dilemmas they face when using their powers. As Yuuki grows more accustomed to his role, he begins to question the nature of his bond with Kyouka and the broader implications of their fight against the Shuuki.

"Chained Soldier" combines action, fantasy, and elements of psychological drama, creating a narrative that balances intense combat sequences with character-driven storytelling. The series explores the relationships between its characters, particularly the evolving dynamic between Yuuki and Kyouka, as they navigate the challenges of their partnership and the larger war against the Shuuki.