Rosetta is a young woman who lives in the capital of Shin-Makoku. She has a father and a younger brother named Risotto. Despite looking like she's about Yuuri or Wolfram's age (maybe even slightly older), her father says she's still a child and can't run his business properly. His business seems to be a restaurant but this is never specified.
One day she found a Maseki on the floor and used it to fix things, so that she could get some money to feed her family. But the thieves who had stolen it from the Blood-Pledge castle, lost it and tried to force her to give it back to them. This is when Yuuri, Wolfram, Conrad and Yozak step in to try and help her.