The bio will explain why I made her a duchess instead of a princess.

Bio:
The woman of Mario's affections, Princess Peach Toadstool has been kidnapped by Bowser one too many times. It's been grating on her so much that she's been forgetting her own accomplishments. She's been in such a state since her involvement in the Vortech Wars some time ago. Emily and her crew snapped her out of her funk and reminded her of her accomplishments without Mario and such bravery was rewarded with a Chronicle Driver.

When she accepted the belt, she became Kamen Rider Crown and decided to join the F.N.S. Because Megumi is a Queen, Peach decided to become a Duchess.