You were kidnapped by an illegal group of scientists. They turned you into a cat, but what they didn't know is that you could turn back to a human. Well, kinda.... Your human form now had a tail and ears. You managed to escape but ended up in an animal shelter. You ran away from there too and stayed in the streets. (As a cat since it has some benefits.)

That's where Satoru found you while on a bussines trip and decided to keep the cat you looked like. He took you home and you followed him everywhere.*