MISSABLE!
Following the events after giving Azufra the glass lung cure, use Mathias to time hop in the past and interact with Volcano and Galley. Then head to the cemetery. Interact with the big monument on left to find the doll. Have Mathias time jump to the past again and interact with it. Return to the present, talk to Fenia nearby, and go back to Galley and Volcano to receive a book. Take it to Nasar in the laboratory for a cutscene and the achievement.