The Shulchan Aruch paskens (OC 554) that it is forbidden to learn most parts of Torah on Tisha Beav, except for a few small sections about aveilut. The question is: the Shulchan Aruch doesn't explicitly mention Hilchot Teshuva, but would it be permissible to do so? The Rambam (Hilchot Taaniot) says that the point of fasts is to do Teshuva. Seemingly learning Hilchot Teshuva would fit directly in this theme. What do you guys think/ do you know of any sources? Thanks so much in advance.
Not only is it permissible, but it is correct to do so according to the Meiri (Moed Katan 21a- Aveilus) . The Meiri explains that learning things that arouses one to do teshuva is a good thing. See Piskei Teshuvos 554:2 for more sources.
Rav Eliyashiv in Ashrei HaIsh page. 485 is quoted as holding that one may learn divrei mussar even though it contains aggada,and Midrashei Chazal since one's intention is not to learn ,but rather arouse oneself to do teshuva which is the obligation of the day.
Text of the Meiri: