Saïx the "Luna Diviner", wields a claymore. His power is derived from moon; his fighting style is a play on the lunar effect and he is somewhat psychotic in nature. The Berserker Nobodies, who wield weapons much like his own, are attributed to him. He has an X-shaped scar on his forehead.
Despite his rank, Saïx is respected as if he were second in command. He is a calm and collected man who shows no emotion, belying his extensively cruel nature. Axel has a clear dislike of him. Saïx becomes the one to brand Axel as a traitor to the group for attempting to derail the Organization's plans for Sora. It is Saïx who captures Kairi after she escapes from Axel and decides to use this to his advantage. After Sora defeated the Heartless army at Hollow Bastion, Saïx appears and
summons even more Heartless for Sora to defeat. Maleficent attempts to use her own Heartless to battle Saïx, but his Dusks quickly dispatch them.
Later, at the World That Never Was, when Naminé helps Kairi escape, Saïx appears to deal with the two, but is stopped by Riku in the guise of Xehanort's Heartless. However, Saïx escaped before any permanent damage could be done. Once Kingdom Hearts neared completion, Xemnas gives him permission to destroy Sora and his friends, and Saïx appears quite happy to be allowed to do so. Despite appearing calm, Saïx shows his true beast-like nature when he fights Sora in the World That Never Was, going into a berserk state by absorbing the moonlight from Kingdom Hearts. After Sora defeats him, he becomes mortally wounded and dies while pining for Kingdom Hearts to give him his heart.
Saïx is voiced by Kirk Thornton in the English version of Kingdom Hearts II and Ginpei Sato in the Japanese version.
"Saïx Deserves more credit than given and you all know it. He's cooler than Axel and all the other bishies."
"Pitiful Heartless, mindlessly collecting hearts. And yet they know not the true power of what they hold. The rage of the Keyblade releases those hearts. They gather in darkness, masterless and free...until they weave together to make Kingdom Hearts. And when that time comes, we can truly, finally exist."