For those of you who struggle on TWTNW Roxas, here's an easy strategy for you! All you do is wait until he RCs you with Dual Stance, force him in the corner (I used Trinity, you're free to choose any method) and spam Quick Run until he's at 1 HP. Then you can use any finisher to kill him.
PS: Don't equip Dodge Roll, otherwise you won't be able to mash Square to spam Quick Run.