This was the only way I could beat that fight (saved right before so I couldn’t go out to level). I was about lv 33, if your around the same level you should be able to get 2-3 turns before Weigraf starts hurting you hp, once that happens just use chakra a bunch until your hp/mp are full again. Keep repeating until he is finally beaten.
Good luck, this was the hardest fight of the game for me.