In a world devoid of color, Sai's mundane school journey takes an unexpected turn when he is transported to an extraordinary monochromatic realm. There, he witnesses a fierce altercation between two girls: a mysterious blonde newcomer and his high school senior, Mikage Mikuro. Upon his return to the real world, the blonde girl reappears as a transfer student, enlisting Sai's help in the battle game 'Over Image' to fulfill her desires. Now faced with a crucial question from the enigmatic girl - 'Are you my foe, or merely an innocent bystander?' - Sai must decide his role in this intriguing new world.