Well, identity is a big theme. Vampire Willow has to figure out who she is now that she's a vampire. Is she still the same Willow? There's also the theme of isolation. In some fanfictions, she is shunned by her former friends because she's a vampire, and she has to deal with being alone. And of course, there's the theme of bloodlust. It's a typical vampire trait, and fanfictions often explore how Willow deals with her new - found urge to drink blood.
One common theme is the struggle between good and evil. Since Willow was originally a good witch, as a vampire, she often battles her new vampire nature which is associated with evil. Another theme is redemption. Many fanfictions explore whether Vampire Willow can be redeemed and return to her former self or at least find a new moral path. Power is also a theme, as being a vampire gives her new powers and she has to learn to control and use them.
The theme of love can be quite common. It could be her love for her old friends in spite of her new vampiric state, or even a new romantic love interest. Another theme is transformation. Not just the physical change into a vampire, but also the mental and emotional transformation. Also, the theme of survival is there. As a vampire, she has to survive in a world that may not be very friendly towards her kind, and she has to find ways to stay alive and thrive.
One common theme is Willow's growth as a character. Writers often explore how she becomes more powerful and confident in the world of vampire slaying. Another theme is her relationships, whether it's with her friends like Buffy or her romantic interests.
One common theme is friendship. Fanfics often explore how Willow and Lemon's friendship develops and endures through various situations. Another theme is the fight against evil. Since it's set in the Buffyverse, they usually team up to combat supernatural threats.
One popular theme is her relationship with other characters. For example, how she interacts with Buffy or Xander in an alternate vampire - filled universe. Another theme is her struggle with her new vampiric nature. Writers often explore how she deals with the thirst for blood and the loss of her humanity.
One common theme is her struggle with power. Given her powerful magic, many fanfictions explore how she controls and uses it. For example, some stories show her learning to master her powers without being corrupted by them.
A common theme is the idea of protection. The angel often takes on the role of protecting the willow, whether it's from dark forces or from the encroachment of a human world that doesn't understand its magic. Another theme is the connection between the spiritual (the angel) and the natural (the willow). It shows how they can interact and influence each other in a fictional universe.
One common theme is the exploration of their unique relationship. Given their different natures, fanfictions often explore how they come to terms with each other. Another theme is power dynamics. Willow has her magic and Spike has his vampiric powers, and stories often play around with how these powers interact.
One common theme is the exploration of their unfulfilled relationship. In the original series, they had a bit of an interesting dynamic that fanfiction often expands on romantically.
Love is a very common theme. Most fanfictions focus on the relationship between Willow and Kennedy, whether it's a new love or a long - standing one.
Friendship is a very common theme. Buffy and Willow have a strong bond in the series, and fanfictions often explore the depths of that friendship, how they rely on each other in tough times.
Love is a very common theme. Since they have a strong relationship in the original work, fanfictions often expand on their romantic love, showing different aspects of it.