As said above ^ Ghirahim is supposed to be the opposite of Fi. Fi is the Master Sword so Ghirahim is the opposite of that, the Anti-Master Sword or the evil version of the MS. Since there is a Triforce symbol on the Master Sword it makes sense that the Anti-MS would have an upside down version of it. It's playing off the whole idea of them being complete opposites.
I think the relationship between Fir and Ghirahim is fascinating, it's like the Yin and Yang. Good vs Evil. One aids the hero the other aids the ultimate evil. It's a dualism that is present between the two and interwoven into the story quite well. I find it to be one of the most interesting parts of Skyward Sword.
theres an upside down triforce on the master sword tooI think it is showing Demise's hatred of everything. Or maybe it is the ANTI triforce o_0. That would open up a whole new realm of possibilities.
it means he hates the Triforce
The triforce represents everything that is good and pure, just like the master sword.
The upside down triforce represent everything that is evil and corrupted, just like the Dark Master Sword that Demise carries..
I'm not so certain they represent anything good at all really. All descriptions and even the triforce itself states that it is incapable of judging between good or evil. It only grants wishes because it is an object. It represents the goddesses that created the land and not really anything else. The demons would know of them and the triforce just as any other spirit or person in Hyrule. And Demise did want to claim it for himself just as Ganondorf in OoT. The triforce was even used to create and maintain a demonic realm in the Dark World in ALTTP. So there really is no judgment or purity present within it. It is just another object of power that could be used by many for their own ends. Only it is the greatest of the objects of power.
The Hylians like to adorn their buildings and creations with a triforce in a way of presenting the power, or maybe channeling its power if not metaphorically. I do not see why it would be any different for demons if they could use it just as well. It is the same as placing a symbol of power on a weapon or shield.
I understand what you are saying and that is actually a very sophisticated statement. Allow me to rephrase what i meant, The master sword is used to defeat Evil, therefore it is used by a person who is good, and would use the triforce for good and pure reasons only. On the Dark Master Sword, it is upside down, because it represents the opposite, that the person that sword belongs to would use the triforce for evil.. Also, the reason the upside down triforce would represent the evil counterpart is because the Original form of the triforce when it is right side up, was created by the Old Gods, whom were good and pure, and would be one day used to destroy evil
Something just crossed my mind, if it is the dark equivalent of the MS, would it have to be forged from a "devil's sword" to work,it would make an awesome prequel (what I mean is, seeing how the enemy's sword powers up in each battle, and Ghirahim gets more powerful, etc), it could go from devil's sword to a longer devil's sword to a devil's sword with a red glow to a dark aster sword, interesting, but on to actual theory, what do you guys think?