Kaoru Ushijima runs Kaukau Finance, a predatory lending operation that exploits desperate individuals with an illegal interest rate of 50% every ten days. The live-action television series is set in contemporary Japan, navigating the murky waters of the country's financial underworld and the social disparities that drive people to ruin.

The series functions as an ensemble human drama where each episode or story arc focuses on a different debtor who has fallen into a specific trap of modern society. Ushijima himself is a cold, calculating, and quietly menacing figure who sees his clients not as people but as products of their own greed and weakness. He is portrayed as an observer of human folly, calmly collecting payments through psychological manipulation and implied threats of violence, often accompanied by his two employees: the brutish but simple Ezaki and the former host Takada, who handles much of the office work.

The first television season introduces the core dynamic of Kaukau Finance and features early storylines involving a host trying to maintain a luxurious facade, a young woman forced into sex work to pay her mother's gambling debts, and a part-time worker who falls into a cycle of borrowing to feed his pachinko addiction. These narratives highlight how a single small loan can spiral into an insurmountable debt trap, leading to prostitution, homelessness, or disappearance.

The second season expands the world by introducing Inui, Ushijima's sharp and amoral childhood friend who works as an information peddler. This season delves deeper into the interconnectedness of the underworld, featuring arcs about a gangster targeting Kaukau Finance's money, a young man aiming to become the number one host in a bar, and a stalker laborer. The series also explores the lives of those who work alongside Ushijima, particularly Takada, who struggles with his own past as a debtor and his loyalty to a job that destroys lives.

The third season adapts the Brainwashing-kun story from the manga, shifting focus to a mysterious man who uses cult-like mind control tactics to enslave an editor from a women's magazine and her entire family. This arc moves away from simple financial need to explore psychological manipulation and the complete subjugation of a person's will for profit.

Alongside the television seasons, the live-action narrative concludes with two theatrical films that follow the third season. Ushijima the Loan Shark Part 3 adapts the Free agent-kun and Middle-aged company employee-kun arcs, focusing on precarious employment and corporate downsizing. The final film, Ushijima the Loan Shark The Finale, adapts the Loan shark-kun arc, which serves as a prequel exploring Ushijima's origins and how he entered the black-market finance business, providing a closing chapter to the overarching story.