Based on a manga series which started off as a one shot manga published in Weekly Shonen Jump under the name "Stray Cat" on October 9, 1999. Then it was greenlit as an ongoing manga series less than a year later under the new title "Black Cat". It was published in Weekly Shonen Jump from July 10, 2000 to June 14, 2004.
Nearly all of the books Eve reads have pictures of cats on them (Including the calligraphy book Sven buys for her.) One book even has a picture of the trio that she is reading to see how to help their situation.
There is a biblical reference with the character names Eve, Adam and Eden.