Kingdom Hearts The Seven hearts and the Six heart blade

What do the Seven Pure hearts do? I just see them as powerful things, like having a keyblade.

Also, the Six heart blade; it was clearly artificial, but what would happen if it was complete?

(Could it be the blade Master Xehanort used?)

 

thats a good question, lol. I dont think that the blade even with 7 hearts that riku had would be powerful enough for master xehanort to use...its only sole purpose was unlocking hearts. technically, it couldnt lock worlds...it couldnt beat heartless or nobodies...it could only steal hearts. makes it seem like a heartless in blade form to me

 

But I think it is all to do with the way the blade was crafted. I am sure that the princesses in the right form would be devestating.