"Cool - Rental Bodyguard" centers on the life of Kakeru, a high school student who becomes entangled in the world of professional bodyguards after encountering a mysterious organization that rents out bodyguards to clients in need. The story begins with Kakeru, an ordinary teenager, witnessing a violent altercation involving a classmate, Rui, who is being targeted by dangerous individuals. This incident leads Kakeru to cross paths with the rental bodyguard service, which employs highly skilled individuals to protect clients from threats.

The organization, known for its secrecy and professionalism, operates under strict rules and employs bodyguards with diverse backgrounds and abilities. Kakeru, despite his lack of experience, is drawn into this world when he inadvertently saves Rui, showcasing a natural talent for protection and combat. Recognizing his potential, the organization offers him a position as a rookie bodyguard, thrusting him into a life of danger and responsibility.

As Kakeru takes on various assignments, he encounters a range of clients, each with unique challenges and threats. These missions often involve high-stakes situations, from protecting celebrities and politicians to rescuing individuals from criminal organizations. Through these experiences, Kakeru develops his skills, learns the importance of trust and loyalty, and grapples with the moral complexities of his new role.

The narrative also delves into the personal lives of the bodyguards, revealing their motivations and struggles. Rui, who becomes a recurring character, plays a significant role in Kakeru’s journey, as their relationship evolves from initial distrust to mutual reliance. Other key characters include senior bodyguards who mentor Kakeru, each contributing to his growth and understanding of the profession.

The story balances action-packed sequences with moments of introspection, exploring themes of duty, sacrifice, and the human cost of protection. As Kakeru navigates the dangerous world of rental bodyguards, he must confront his own limitations and the ethical dilemmas inherent in his line of work. The series maintains a steady pace, blending intense confrontations with character-driven storytelling, making it a compelling exploration of the bodyguard profession and its impact on those who choose it.