Zenryaku. Neko to Tenshi to Doukyo Hajimemashita.

On his way home, a high school teacher, Satoru Mizukami, found three cats and Mio, a girl around 15 years old, abandoned on the side of the road and took them home. Although Mio remembered very little about herself, she was able to communicate with the cats, and her otaku-related knowledge was astounding. This was all because of an evil scheme by the angels in the heavenly realm. What is the fate of Mio, Satoru, and the cats?

(Source: HJ Bunko, translated)