It's on Quizilla.com and I've read it two years ago. I didn't read the sequel cuz I thought the new girl (short black hair) would take Hiei away from the first sequel. The second sequel is when Hiei's gf (or whatever) goes to America for a year or two (Koenma sends her). The girl from the first sequel was a "thief" or something in demon world when she really worked for Koenma. I think she took Yusuke out to demon world or something. So yeah...here's a pic from the girl in the second sequel. I hope you know what I'm talking about lol anything helps! Minus bad comments, saying "idk" or whatever lol thanks 
http://media.photobucket.com/image/anime+black+cat+girl+/VampireBloodrace1441/Anime%2520Girl/GirlwithBlackCat.jpg
I hope this helps!
http://media.photobucket.com/image/anime+black+cat+girl+/VampireBloodrace1441/Anime%2520Girl/GirlwithBlackCat.jpg
I hope this helps!