It's at the succubus Tower is where you get the mana you have to become friendly with Rena and then you can request lessons in one of them will result in you gaining mana as well as a skill. You can also get skills from talking to the clerk at the bath house and become friendly with her and then you can spar with her and that is how you get a skill. The final skill that I know of you gain from by going to the bar that is in the slums and requesting the house special on the rocks which will allow you to enter the basement of the bar. Where you then have to fight through multiple people and eventually you will fight lin lin and eventually after two or three potentially even four fights with her you will gain a skill from her. Other than that I do not know. I hope that this was helpful to you.