Additionally, you'll unlock skill points which can be spent on new abilities to help you in battle. (heypoorplayer.com)
When the bar fills up, it gains a level and also unlocks a skill which can then be used on your character. (dualpixels.com)
I really liked the aspect of unlocking skills and becoming more powerful, and achieving a higher level of freedom as you become more powerful. (blog.us.playstation.com)