I'm pretty sure I have this story saved but I can't seem to find it. I remember only this one scene where Kagome is challenged by another youkai and they go to an arena to fight it out. She spends most of the time running all over the arena floor, taunting her opponent by saying she could do this all day, etc. When she finally stops running, the youkai tries to finish her, only to be blasted by a column of her power. She had been running all over the arena, imbuing the ground with her powers. As soon as the youkai stepped on/near one of her footprints, he got blasted. He would keep healing but keep being blasted. He goes through a cycle of being hit with purification powers from the ground to trying to heal. Does this ring a bell? Thank you!

That´s Reserve Untapped by SilverEyedHyuuga

It is rated MA

It's in chapter 24 of Reserve Untapped. Just finish read it yesterday

Thank you both! Good timing on your part Erin!