Game description from the publisher:
You've entrusted your nine courtiers to deliver a beautiful love letter to Princess Persephone, but your opponent also has nine courtiers delivering an equally moving love letter to the same princess! In each case, eight letters are decoys and only the letter with the red seal is the "true" love letter. Intercept your rival's true love letter to make sure that only your letter sways her affections.
In Mirror, Mirror each of the three types of Character pieces carries a letter, has a mirror on the back of the piece, and has a special way of moving on the board similar to chess. When your piece lands on an opponent's piece, you must say what color seal is on its letter. If correct, that piece is removed from play; otherwise your piece is removed from play. Choose carefully and make liberal use of your mirrors to discover the color of the seals on your opponent's pieces before venturing to intercept their letters.