Bakeneko Katatte Sourou

Matoi Souta is an overworked office worker tired of his life. Then, on his way home from a long day of work one day, he decides to watch a traditional Japanese play. But something strange happens. He could have sworn he saw one of the actors has cat ears.
It turns out that the man is actually a bakeneko -- a shapeshifting cat from Japanese folklore. And then, the cat speaks: "From now on, you will be my spouse."
(Source: Tokyopop)
Note: The chapter count includes an extra story.