Fionna

Fionna (or Fiona) is the gender-swapped version of Finn, created by series designer Natasha Allegri. She is usually seen in the company of her own stretchy companion, Cake who is the gender-and-species-swapped version of Jake. Fionna's enemy is the gender-swapped version of Ice King, the Ice Queen. It was revealed on April 6, 2011 that the working title of the sixth episode in season three is "Adventure Time with Fionna and Cake."

Appearance
She sports an outfit similar to Finn's: a rabbit-themed hood (opposing Finn's bear-themed hood), exposed locks of blonde hair, a sky blue shirt and dark blue skirt, which are a lighter shade of blue than Finn's clothing, the same green backpack, athletic socks that have two blue stripes at the top, and Mary Jane shoes. Like Finn, she occasionally wears a yellow sweater while in the Ice Kingdom. While Finn had a sword made out of gold, Fionna has a sword made out of ruby. It should be noted that she has a much thicker, curvier figure than most other humanoid females seen in the show (save Susan Strong), with wider hips and thicker legs. This could be a reference to her status as a warrior, or a device to greater show gender differences between her and Finn. Natasha refers to this as "chubby cute".

Trivia

 * Similar to Finn and his cracking voice, Fionna also seems to be going through puberty as shown in "PMS Time with Fionna and Cake!"
 * Only other human besides Finn left in all of Ooo, a long-lost sister of Finn, an ancestor of some sort, or simply exists in a separate universe.
 * Fiona may have been adopted by Cake's parents, like Finn being adopted by Jake's parents.