Utsuro Naru Regalia

In a world where 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...
(Source: Yen Press)