User blog comment:IamJakuhoRaikoben/Chapter 457: Naked Battle, Review./@comment-4999650-20151019120400/@comment-7418318-20151019130547

As short as the broken tip is, it's barely enough to get through the skin, much less cause a debilitating or fatal wound. Lucy could probably deal more (physical) damage with her finger-nails than with Aquarius' broken key.

Then there's also the suspiciously big "light-reflection" from the key. Why would the key make such a big star-shaped reflection? I think Lucy might have been doing something magical, rather than just a regular stabbing.