"Chained Soldier" is set in a world where humanity faces constant threats from mysterious creatures known as Shuuki, which emerge from portals called Mato. These portals appear randomly, and the Shuuki wreak havoc on society. To combat this, an elite military unit known as the Anti-Demon Corps is formed, composed of individuals who wield special powers granted by Peach, a rare fruit that grows only in Mato. These powers, however, come at a cost: the users, known as Peach Bearers, are bound to a "Chain" system, which limits their freedom and forces them to obey strict commands.

The protagonist, Yuuki Wakura, is a young man who inadvertently becomes a Peach Bearer after a Shuuki attack. Unlike others, Yuuki's abilities are unique, as he can absorb and neutralize the powers of other Peach Bearers, making him both a valuable asset and a potential threat. He is paired with Kyouka Uzen, a skilled and determined commander of the Anti-Demon Corps, who becomes his handler. Their relationship is central to the narrative, as Kyouka struggles to balance her duty to control Yuuki with her growing trust in him.

As the story progresses, Yuuki and Kyouka face numerous challenges, including internal conflicts within the Anti-Demon Corps, the moral implications of the Chain system, and the ever-present threat of the Shuuki. The series explores themes of power, control, and the cost of survival, as the characters grapple with their roles in a world where freedom is sacrificed for safety. The narrative also delves into the origins of the Shuuki and the Mato portals, revealing deeper mysteries that tie the fate of humanity to the actions of the Anti-Demon Corps.

Supporting characters include other members of the Anti-Demon Corps, each with their own motivations and struggles, as well as antagonists who seek to exploit the Peach Bearers for their own gain. The dynamic between the characters drives much of the plot, as alliances are tested and loyalties are questioned. The series balances action-packed battles with moments of introspection, creating a narrative that is both engaging and thought-provoking.