A colourless world, a pure white world, a world where everything is filled with only one colour. During what ought to have been a young man's usual walk to school, Sai was suddenly blown away to such an extraordinary world.

There, he witnesses 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, a senpai at his high school. Then, the blonde girl appears 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 seems to have come to seek out Sai to be her companion.