Utsuro Naru Regalia

A young man named Yahiro lives in the remnants of Japan after a dragon nearly eradicated the population. He survives by salvaging in the ruins. One evening, after escaping a deadly creature called a Moujuu unharmed as usual, he discovers two unexpected visitors at his home—twin girls named Giuli and Rosé. They identify themselves as art dealers and present him with a request.