User blog comment:Miskos3/Fairy Tail 526: My Name Is..., Review/@comment-68.102.118.10-20170313072127/@comment-7418318-20170314070235

I think the Anon meant when Lucy used the Aquarius Star Dress during the fight against Brandish.

But then it was "only" Star Dress, so while the boken key might not enable Lucy to fully summmon Aquarius, it might still hold enough magic to use Star Dress. If the remnants of the key still holds a small amount of it's original power and is still connected with Aquarius, it would certainly explain how Aquarius was able to summon herself to Lucy's position and know that Lucy was in danger in the first place.

Of course that could also have been the other spirits sensing the danger, telling Aquarius and guiding her to Lucy... but that seems a bit far-fetched. Why risk Lucy's life with such a round-about way instead of intervening themselves.

Then there's also the matter of how Lucy attained Aquarius Star Dress the first time. That direct intervention by the Spirit King after the key was already broken, might have changed the rules for this particular Star Dress. With the tattoo coming and going it's possible that the power of this one Star Dress was imbued directly into Lucy enabling her to use it even without the key.

Mind you, I'm only talking about possibilities here, since we barely know anything for certain when it comes to the matter of the broken key and Star Dresses in general.