This is for those without a boost partner or turbo pad.
I played Quick battle as Xiba as he has a Y+B move which blocks all horizontal attacks and does not use Soul gauge.
An impact is counted when you deflect the opponents attack with a Guard impact move.
The opponent I found is called vonCorra she is a D1 grade, and her title is Horizontal Flash, she is slow enough that you can press Y+B before most of her horizontal moves, and her first move would normally be a horizontal attack. I was getting 5 or 6 impacts a round.
This is my first tip, so please let me know if I can improve this to make it better or clearer, and I hope this helps you.