A street-smart, tricky boy Remi meets and befriends in the streets of Paris. He knows how to play quite a few instruments as well. He's lived in Paris most of his life, and isn't used to travelling.

After Remi departs from the Acquin family, Mattia joins him in in his travelling. Mattia was born in Italy, but doesn't remember anything of it and knows absolutely zero Italian. His mother is dead, and he feels Remi is lucky to have a mother. When Remi and Mattia meet up with a music teacher, it is revealed Mattia is a musical genius. He later goes on to have a successful career in music.