Is Tish'ah B’Av a Day of Teshuvah? (Yes & No & Yes)

We revisit and revise our thoughts on this very important question. We don't recite Selichos on Tish'ah B’Av as we do on other fast days. We mourn on Tish'ah B’Av. But, what if there is another element to the day? If Teshuvah is a key component of Tish'ah B’Av, how do we express it differently on this most unique day on our calendar? What is the key difference between Yom Kippur and Tish'ah B’Av?