Redjuice (from redjuicegraphics) is the artist, so the wallpaper is in the correct category. We know it’s from Bakemonogatari, but in this case the artist who made it gets priority.

I’d say that overall you did fine. Some suggestions…

The concrete wall in the BG could’ve been a bit more interesting as far design goes (cracks, dirt, graffiti, etc etc). That graffiti you got there with you name would’ve look better if it was incorporated into the wall itself. Make it part of the BG. Also, I’d have the wall a bit less blurry…

Lighting around the character (in the whole scene for mater fact) could’ve been a bit more dramatic and less even. Her shadow on the wall could use more darkening.

Seeing that she is a vampire (500 years old and counting), it would’ve been interesting if things were more “gruesome” as far concept goes. Anyways, your concept still works perfectly… just saying it would have been interesting to see a darker approach for it, that’s all.

As a final note, kudos on your painting. Keep it up and I’m sure you’ll be painting better in no time.