Hailing from Hokkaido, Japan's northernmost island, Kōjirō Tanne moves to Tokyo, insisting on bringing his cherished talking horse, Hikarikin. Described as an "idiot boy," his life takes an unexpected turn when Rel, an alien king from planet Wedelun, provides him with a transformative belt. This belt grants enhanced physical capabilities—increased strength, speed, and visual perception—theoretically enabling him to function as a "Miracle Hero" tasked with protecting Earth from extraterrestrial threats.

However, Kōjirō displays minimal interest in heroic duties or global protection. His focus centers almost exclusively on leveraging the belt's abilities to impress classmate Yuka Ichinose, for whom he develops an immediate infatuation upon meeting her at school. This pursuit manifests in comically exaggerated attempts to gain her affection, complicated by a rivalry with Michinari, who also seeks Yuka's attention.

Kōjirō's consistent misuse of the belt frustrates Rel, who intended the device for planetary defense, not romantic pursuits. Adding to the dynamic is Hikarikin, who exhibits jealousy whenever Kōjirō interacts with other girls. Characterized by impulsiveness and a lack of forethought, Kōjirō frequently triggers chaotic or absurd situations driven by his singular focus on Yuka and misinterpretation of the belt's purpose.