Hollow Regalia vol 1 back

In a world where there the Japanese people were almost completely wiped out by a dragon, Yahiro spends his lonely days working as a salvager in the ruins of Japan. One night, despite being gutted by a Moujuu, one of the monstrous beasts that roam the ruins, he makes it home without a scratch on him, just like he always does. But on that night, he finds he has unexpected guests, two twin girls named Giuli and Rosé. And this pair of supposed art dealers has a request for him...