Hey, that's not Zephyr! Once a certain point in the game is reached, Zephyr can be removed from the party. Thanks to WCouillard, other characters can now also appear on the back of Winter.
Yup, I already had it implemented for changing the sprite to show Zephyr riding Winter, so it's mostly just a matter of tossing other characters onto Winter's sprite. About 5-10 minutes per character, so not bad!
Maybe Jasmine got tired of this new guy in charge, punched him straight in the gut, and took off with his Chocobo while giving the rest of the team the lali-ho.