A colorless world, a pure white world, a world where everything is filled with only one color. What ought to be a young man's usual route to school—Sai was suddenly blown away, it was such an extraordinary world.
There, he witness two young girls' fight unfold before him. One of them is a blonde girl he has never seen before, and the other is Mikage Mikuro, an upperclasswoman in his high school. Then, the blonde girl appeared as a transfer student before Sai, who has just returned to the original world. In order to grant her wish, she joined the battle game "Over Image" on her own and now she seem to have come to sought out Sai to be her companion.