Spoiler A Curious Trait of Ghirahim.

[Moonlight]

In my own opinion I believe he is half Siren half Hylian, and he may be ashamed of that so he calls himself a demon because of being half of two species. The round ear that is hidden may explain his shame of being half of two species. So yeah that is my theory though somebody might have something similar to that...

 

[Cabbage]

Aonuma Nintendo Power interview pretty much confirms that he's the antagonist in the game, and another 6 sub-villains simply wouldn't fit.

I still think it could be that. He could be one of the seven sages gone bad or something similar, (Although that is rather doubtful,) or perhaps the other 6 peoples died or something else.

 

[Lord Death]

Hmm I like the hybrid idea. They could call this game "The Legend of Zelda and the Half-Blood Prince."

 

[Moonlight]

Hmm I like the hybrid idea. They could call this game "The Legend of Zelda and the Half-Blood Prince."

That made me laugh! It is totally true! also btw I love soul eater!