Saïx is also known as "The Lunar Diviner", the seventh member of Organization XIII with Moon as his attribute; although his rank is actually that of the second-in-command. He wields a claymore called "Lunatic" and controls the Berserker Nobodies. He makes numerous appearances in Kingdom Hearts II, confronting characters in Hollow Bastion and Twilight Town.
In Kingdom Hearts: 358/2 Days, Saïx and Axel are revealed to have somewhat of a connection. In the game, they are planning to overthrow Xemnas together, and it is revealed that the massacre at Castle Oblivion was orchestrated by both of them. When they are talking about the fate of Xion and Roxas, Saïx calls Axel by his true name, Lea, showing how they did indeed know each other well before becoming Nobodies. Despite being a traitor, Saïx is the one who gives everyone their missions for each day, speaks on behalf of Xemnas, and chooses who partners with who on certain missions throughout the game.
As a boss he appears in both Kingdom Hearts II and 358/2 Days. In 358/2 Days he is defeated but not eliminated by Roxas as the boy chooses to leave the Organization for good.
In Kingdom Hearts II he is depicted as truly emotionless after he makes Sora beg him just to see how he would do in order to free Kairi. He is defeated by Sora in The World That Never Was and is the last Organization member to be fall before Sora faces Xemnas, the Superior of Organization XIII. While dying he wonders why he hasn't obtained his heart after all he has done.
Appearance in Kingdom Hearts Birth By Sleep
Saïx's complete being, Isa, appears briefly on the world of Radiant Garden in Kingdom Hearts: Birth By Sleep alongside his friend Lea and meets Ventus.
He is a member of the 13 seekers of darkness. He is one of the few members to be loyal to Xehanort.