In Vampire Knight Yuki x Kaname fanfiction, a prevalent trope is the transformation trope. Yuki's transformation from a human to a vampire and how that affects her relationship with Kaname is often explored. Additionally, the 'redemption' trope can be seen, where Kaname might be portrayed as a character in need of redemption for his past actions, and Yuki is the one who can bring about that change. These tropes help to create engaging and unique stories within the fanfiction realm.