1. An anagram for "mansex."
2. Leader of Organization XIII.
Xemnas = Mansex.
Kind of like how Xigbar's name can be rearranged to Bigrax.
Number 1 of Organization XIII
Also known as the "Seeker of Darkness"
Previously known by fans as the Enigmatic Man, Xemnas (whose name is an anagram of Ansem’s name with an 'X' added to it) is the Nobody version of Xehanort. Like his counterpart, Xemnas is collecting hearts but he intends to absorb Kingdom Hearts to become an complete and almighty, godlike being. He can manifest some sort of energy as a weapon (one of the ways he uses it is by making red "lightsabers" with it), use the element of darkness, control the Sorcerer Nobodies and move through solid objects such as humans.
He is the man whom Sora fought in the Final Mix version of the original Kingdom Hearts at Hollow Bastion; he was the first member of the Organization that could be fought. Xemnas is first seen in Kingdom Hearts II during the beginning at a beach in the World of Darkness, stating that Roxas looks like Sora and asks if he has met him. Later on, he appears in front of Sora at Hollow Bastion to taunt him, and then later at Hollow Bastion again when the enormous Heartless army attacked it. While he escapes, Sora confronts him again in the World That Never Was. He is the last member of the Organization that Sora battles in Kingdom Hearts II; it is done with the help of Riku.
He is voiced by veteran seiyu Norio Wakamoto in the Japanese version of Kingdom Hearts II.
Xemnas isn't as tough as he's let on to be, however his attack where he traps Sora is annoying.