Well, my unic skill is observation as you can see and I cant add another one because I actually dont have it))
Did you open up the menu and set the normal attack skill?? If not follow the following steps.
1. Open up the game menu by pressing either the 'x' or 'esc' key.
2. Scroll down to the option 'Skill Set' and press the 'z' key.
3. Press 'z' again to select Yua. You are now on the skill select screen.
4. Press 'z' again to edit what will show up in the Skill menu during combat, and add the Normal Attack skill.
If these steps don't solve the problem then you have a bug and I would suggest starting a new game. If that doesn't fix it then you may need to download a new copy of the game.