Shuto Katsuragi, a fifteen-year-old with a burning desire to become a superhero, faces one seemingly insurmountable problem: his diminutive stature. In a world where superhuman abilities can be granted and commercial heroes with corporate sponsorships dominate the public eye, the Hero Association licenses these costumed champions, turning crime-fighting into a blend of spectacle and marketing. Shuto, an energetic otaku of hero culture, is frequently teased for his height and his dreams, especially when he tries to emulate his idol, the legendary hero Shiningman.

The story takes a sharp turn when Shuto is abducted by the enigmatic evil organization Jackal after a seemingly staged encounter where a hero appears to rescue his classmate, the quiet and beautiful Mirea Mizushima. Tricked into signing a contract and donning a transformation watch, Shuto is horrified to discover that the entire rescue was a setup and he has become Jackal’s new super-powered pawn: Ratman, a dark and tall anti-hero. The organization, led by Mirea's older sister Crea, forces him to work for them in their shadowy mission to overthrow the Hero Association, which they believe is responsible for a hidden crime against their family. Despite being branded a villain, Shuto resolves to use his new identity to uphold his ideals of heroism, which puts him on a collision course with the very system he once admired.

The central conflict arises as Shuto navigates his double life. At school, he is a short, aspiring hero, but at night, he is the fearsome Ratman, forced to carry out Jackal’s schemes. This brings him into direct conflict with Rio Kizaki, the daughter of the Hero Association's president and a registered hero who is also his upperclassman. Shuto’s journey forces him to confront the blurred line between good and evil, as he discovers that many licensed heroes are selfish and popularity-driven, while the "villains" of Jackal have their own complex, sympathetic motivations.

A major narrative arc involves Shuto’s internal struggle with his own powers and identity. He taps into his inner potential, recreating Shiningman’s legendary "Shining Ray" technique, proving that true heroism is not about a license but the will to protect others. He is supported by the speechless and comically inept Jacky Combatants, whose seemingly useless nature provides both humor and unexpected loyalty. As the story progresses, Shuto must stop a corrupt conspiracy within the Hero Association, rescue those he cares about, and ultimately decide what kind of hero—or villain—he truly wants to be, all while trying to get a year's supply of free pizza from a portly local hero named Fatman.