"Plunderer" is set in a post-apocalyptic world where individuals possess "Counts," numerical indicators tied to their identities and actions. These Counts can represent anything from the number of kilometers walked to the number of people one has killed. When a Count reaches zero, the individual is dragged into the Abyss, a mysterious and feared void. The story centers on Hina, a determined young woman searching for the legendary "Ace," a hero her mother spoke of before disappearing into the Abyss. Hina carries a sword that belonged to her mother, which bears the inscription "Ace."

Hina's journey leads her to Licht Bach, a perverted and seemingly lazy man who hides his true identity as the Ace, a legendary warrior with a Count tied to the number of women he has kissed. Licht's Count is dangerously low, and he is reluctant to reveal his past or his abilities. Despite his flaws, Licht becomes Hina's protector and guide as they travel together. Along the way, they encounter Jail Murdoch, a stoic and powerful soldier with a Count tied to the number of people he has killed, and his sister, Lynn May, who harbors deep affection for Licht. The group is pursued by the Althea Empire, a militaristic regime that seeks to exploit the Count system and maintain control over the population.

As the story progresses, the true nature of the Counts and the Abyss is revealed. The world was once governed by advanced technology and a system called the "Ballot Box," which assigned Counts to individuals based on their actions. However, the system was corrupted, leading to societal collapse. The Abyss is revealed to be a gateway to another dimension, and the characters uncover a conspiracy involving the Althea Empire and the remnants of the old world's technology. Licht's past as a soldier and his connection to the Ballot Box play a central role in unraveling these mysteries.

The narrative explores themes of identity, redemption, and the consequences of power. Hina's unwavering determination and Licht's gradual acceptance of his responsibilities drive the story forward, while supporting characters like Jail and Lynn add depth to the world and its conflicts. The series balances action, humor, and emotional moments, creating a dynamic and engaging narrative. As the characters confront their pasts and the forces seeking to control their world, they must decide whether to uphold the flawed system or fight for a new future.