In such fanfiction, Yuuki might be depicted as more alluring and perhaps more assertive in her relationship with Zero. Zero, on the other hand, could be shown as more brooding and possessive. However, this is a very general view and can vary greatly depending on the author's interpretation.
Kirito is more of a traditional swordsman in terms of his combat style. He often relies on his sword - fighting skills and his ability to quickly analyze his opponents. Yuuki, on the other hand, has a very unique and flashy fighting style. Her movements are more acrobatic.