Ah yeah, that's 'fight' is harder the higher your corruption is.
You need to body-block the lights, each of which does about 15% of your health in damage to you and lowers your corruption slightly.
You may need to heal up using herbs and such from your inventory between hits
Make sure the wisps don't hit the other person (If they do it does 50% of your health in damage)
The event ends when you hit 0 corruption