User blog comment:IamJakuhoRaikoben/Chapter 457: Naked Battle, Review./@comment-4999650-20151019120400/@comment-1359322-20151019151148

Well Lucy was probably thinking that if she can inflict even a minor wound on Brandish it might be helpful on later battles. Even if its only 1% it's still better to face an opponent that is not 100% after all.