Origin

Saïx real name is Isa. Before he became a nobody, Xehanort gave Isa a part of his heart. Under Xemnas control, he had much power and was extremely mysterious. Saïx and Axel never got along very well, as he was all for order, and Axel was wild and jumpy all day, any day.

Major Story Arcs

This did not please Saïx or Xemnas at all, as he had no emotions to display. Therefore, he kept the two Organization XIII members away from each other as much as possible. Saïx kidnapped Kairi, and she was kept prisoner for a majority of Sora's adventure after reawakening. While she was there, Saïx and her talked about a lot of things as Saïx rarely had to go out into battle on his own. She asked him about lots of things, but mostly about what "Kingdom Hearts" really was. He never told her, but only gave her the really bad news about it: That Sora was helping them get one step closer with each move he made. Every time Sora killed a heartless with the Keyblade he sent their energy up to The World that Never Was, a place that Organization had been using as their headquarters since they were brought into action and realized who and what they were.

Saïx was confronted after by Sora. However, after revealing what he had told Kairi to Sora, Sora lost motivation to fight him, as each move he made sent them closer to their goal.

In The World that Never Was Saïx was encountered in the "Addled Impasse" chamber of the castle where his final battle took place by absorbing the power from the Kingdom Heart's moon. This gave Saix the beserker power and he used savage attacks on Sora, Donald, and Goofy. In spite of that he was defeated. In the end all he wanted was a heart.