"Wanna Be Hero" centers on a young man named Hiroshi, an ordinary high school student with aspirations of becoming a hero. The narrative begins with Hiroshi encountering a mysterious artifact that grants him extraordinary powers, thrusting him into a world of supernatural threats and moral dilemmas. As he navigates his newfound abilities, Hiroshi is mentored by a seasoned hero named Kenta, who teaches him the responsibilities and sacrifices that come with being a protector of humanity.

The story unfolds in a contemporary urban setting, blending elements of action, drama, and coming-of-age themes. Hiroshi faces a series of escalating challenges, including battles against malevolent entities known as "Shadows," which threaten both the physical world and the balance of human emotions. These Shadows are manifestations of negative human emotions, and their defeat requires Hiroshi to confront not only external enemies but also his own insecurities and fears.

Key characters include Hiroshi's childhood friend, Aiko, who provides emotional support and a grounded perspective, and Riku, a rival hero with a contrasting approach to justice. The dynamic between Hiroshi and Riku evolves from antagonism to mutual respect as they work together to combat greater threats. The narrative also explores the origins of the artifact and its connection to an ancient conflict between heroes and a powerful antagonist seeking to exploit its power for destruction.

Themes of self-discovery, responsibility, and the duality of human nature are woven throughout the story. Hiroshi's journey is marked by personal growth as he learns to balance his heroic duties with his everyday life, grappling with the consequences of his actions and the impact they have on those around him. The series concludes with a climactic battle that tests Hiroshi's resolve and forces him to make a pivotal choice about his future as a hero.