Beyond Heaven's River — Greg Bear

THE LAST VETERAN

Kawashita had passed up the chance to die honorably, to go down with the mortally wounded carrier Hiryu. He was sure he had made the wrong choice when the alien spacecraft plucked him from the sea near Midway -- now he would certainly die, but alone and without honor.

But the aliens did not kill him. Instead, they gave him a world of his own, a world in which he was supreme master, allowed to re-create and alter history, to indulge any fantasy.

Then suddenly he was once again among humans -- to whom World War II was a half-forgotten memory, four centuries past....