Tsukasa Mendō is an ambitious 11-year-old determined to become the world's greatest player of Gigant Shooter, a competitive card battle game resembling menko or pog. His journey focuses on mastering this game with his primary battle partner—the special menko card "King Menger" inherited from his father. This card holds profound personal significance, deeply connecting his motivation to his family.

He navigates this quest within a close-knit circle of fellow Gigant Shooter enthusiasts. This group includes Miruko Koide, characterized as cute yet tsundere; Manabu Numata, a bespectacled individual with bully-like tendencies; and Ataru Dōmoto, a sharp-tongued realist. Their shared passion for the game forms the core social dynamic surrounding Tsukasa's competitive pursuits.