Based on the light novel series of Masahiro Yusa.
Here's a synopsis provided by the scanlators of the manga:
A colourless world, a pure white world, a world where everything is filled with only one colour. What ought to be a young man's usual route to school - Sai was suddenly blown away, it was such an extraodinary 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, a senpai at his Highschool. Then, before Sai, who returned to the original world, the blonde girl appeared as a transfer student. 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 campanion. "Two points. Are you my enemy? Or are you a harmless citizen?"
There are currently four chapters translated as of this date, and I've got to say that I'm liking the story thus far. Nice art style, a good premise and an MC with an ability that reminds me a lot of a certain unlucky spiky haired boy.
I'm really looking forward to where this manga (or in this case, the light novel it's based on) would eventually go.