I would suggest leveling up more but more importantly leveling up your Drives. Learning the moves from them (like Double Jump & Slide) plus making them and yourself more powerful helps the battle. Put Potions and make them Auto Equip (so they can keep using them) and buy a ton. Other then that just beat the hell out of him with Valor and Dodge. All I can suggest. I was level 40 when I beat him I think.