what i don't understand is how girahim can feel emotion and has a personality, while Fi can and does not. Perhaps The demon Lord was originally the mastersword gone rogue, Thoughts?
Unlike Fi, Ghirahim isn't very dependent on Demise. Where as Fi is very dependent on Link. Ghirahim is able to use his abilities as the anti-master sword to resurrect Demise, capture Zelda/Hylia, and or face Link. Fi on the other hand can't fight, but is extremely intelligent and is willing to inform Link on his current situation and circumstances, such as telling him about Silent Realm's and enemies. As for emotions, it's debatable on that subject. Fi DOES have some emotion at the VERY END of the game. Although, the two of them do differ on that stance.
And yes; both of them are VERY similar. And I would love to see not only a confrontation between the two, but also a dance off.
Haha!