Neko no Manimani

One rainy day, unsuccessful novelist Matabi adopts an injured cat she found on the road. However, the cat turned out to be a 1200-year-old Nekomata, a youkai capbable of transforming into a human. Capable of speaking human language and with the appearance of a pretty girl, she introduces herself as Kaneko. Having run dry of material for her work, Matabi feels a faint hope that she may get some new ideas with Kaneko around. However, her rowdy days are just beginning... (Source: Kadokawa, translated)