Ah, one of Monty's earlier works.
It's supposed to be one of the winning dressphere designs for the Rikku v. Ayane fight.

That's meant to be Sonia, a character from Ninja Gaiden, and a possible opponent. Of course, that image was made a while before Ninja Gaiden II came out. When it did come out, it became clear that Sonia could barely hold her own in a fight, and would be an awful addition to Dead Fantasy (at least, in my opinion).

Fortunately, Ninja Gaiden: Dragon Sword offered a much better alternative in Momiji, who is better for a number of reasons:

1. Unlike Sonia, she can actually fight. She is Ryu Hayabusa's protégé, after all. She wields the Heavenly Dragon Naginata quite gracefully in Ninja Gaiden Sigma 2, which brings me to my next point.

2. She offers much more variety than Sonia. Much like how Kairi's abilities are largely derived from Sora's, Momiji could draw from many of Ryu's abilities. With his ninpo, and all of his weapons, Momiji would be the perfect counter to Kairi and her multiple Drive forms.

3. The pairings in Dead Fantasy are based on the characters themselves, and aren't just random, or based on weapons. Yuna and Kasumi, Rikku and Ayane, Tifa and Hitomi, and even Rinoa and Rachel, are more alike than most people seem to think. Momiji and Kairi is more in line with that theme than Sonia and Kairi. In fact, I remember a user by the name of Alzrius once wrote a lengthy piece on just why they make such a good pairing. It was an interesting read, though I think it would be impossible to find at this point.

Of course, this is just speculation. No one knows if Monty has actually changed his mind, though with Momiji's appearance in V, I'd say it's a safe bet he has.