So Skills will all vary based on your character as well. 

For instance, Physical Skills will cost less MP and be more effective in the hands of physical characters. 

Mental skills will cost less MP and are more effective in the hands of mental characters (this being magic and stuff). 

So lets take the Counter Skill for instance. In Tim's possession it costs 6 MP, but in the hands of someone like Rainer it would cost less. 

This sort of creates a way to customize your characters as your skills will all vary depending upon what you make your character into. You may even find yourself getting special unique skills upon reaching certain milestones depending upon how you have grown your character. 

This gives a level of character customization.