Uchinukareta Senjou wa, Soko de Kieteiro: Dangan Mahou to Ghost Program

The power to rewrite history...and all it costs is a deal with the devil. For a hundred years, the East and West have waged a ferocious war using everything from tanks to witchcraft, but the technological advancements of the West have begun to shift the balance. That all changes one day when Rain Lantz, a young soldier from the East, finds a few mysterious silver bullets--and discovers that anyone shot with them is erased not only from the battlefield, but from history itself. Soon after, he meets the bullets' creator, a Ghost who calls herself Air, and learns that if he wishes to continue using this power to end the war for good, he will have to give her his freedom... (Source: Yen Press)