Yeah... The entire point of this contest is to effectively describe a character. I am sure that if somebody entered a rock as a character, but described it in a way that brought it to life, and connected with the members of ZFGC, then it would win. As Star said the point of this contest isn't about the strength of the character physically, but rather the strength of the character description. I'd say go ahead and enter your idea, but be sure to add character to your character instead of just muscles.
Also - Obviously you wouldn't want to add a character that is an exact clone of Sephiroth either, as the point of this contest is to make your own character... I am sure you already knew that though.