Mary's now a third-year at school, which means she'll finally get to settle down and relax, right? Wrong! She comes up with the bright idea of turning the school's martial arts tournament into an academy festival, then His Highness Prince Reifus ropes her into running security for the event. That wouldn't be so bad, except that Her Majesty the Queen decides to visit the festival—which leads to Her Majesty's mischievous childhood friend, Princess Emilia from the demon kingdom, showing up to fly around and cause all sorts of mischief! And if that weren't enough, mysterious intruders are spotted among the crowds... How will Mary get out of this little pickle? Follow the invincible little lady as she dons her silver armor and fights for her friends, but just remember—she's definitely not the Argent Knight!