Hollow Regalia, Vol. 1 (manga)

In a world where Japanese people were almost completely wiped out…Yahiro spends his lonely days working as a salvager in the wreckage of Japan. Despite routinely being gutted by Moujuu, the monstrous beasts that roam the ruins, he makes it home every night without a scratch on him thanks to his body’s mysterious regenerative powers. But one evening, he’s ambushed by twin girls named Giuli and Rosé. And these supposed “art dealers” have a dangerous mission for him—something only he can help them with.