Final Fantasy XV is a big deal for us here in the US, but we pale in comparison to the hype train over in Japan. The game is in the midst of a massive marketing push in the weeks leading up to its release (yes, the release is official) and the latest issue of Weekly Jump showcased an all-new guest character that will at least temporarily pop in during Noctis' journey.
Here is the page courtesy of Nova Crystallis:
It's a bit difficult to tell, but the bottom right image shows off the new character, whose name is Iris Amicitia. She is the younger sister of your party's mainstay companion, Gladiolus. Iris uses her fists in combat (think Tifa/Zell) and can also user her giant Moogle to attack (and that thing is BIG).
If you are one of those worried about the game not featuring anyone with two X chromosomes, Square Enix is currently kicking around ideas for DLC featuring the game's female characters, so you don't have to worry about getting an overdose of bro-tacular broness. Bro.
Source: [Nova Crystallis]