personalitySaix, staying true to the same feelings of Xemnas, appears to be one of the few Organization members who can sincerely be called a "nobody." Though he claims to Sora in Kingdom Hearts II that he is special because he "remembers what it's like to have a heart," his personality shows otherwise. He's one of the coldest members of the Organization. He is one of the most professional characters as well, never losing his cool until the final battle. Saix understands what it means to be a nobody, or nothing. He doesn't attempt to be something he isn't, unlike the majority of the Organization. He uses his past memories to manipulate Sora and others to do what he wants, making him beg to see Kairi even though he refuses his request. Saix also easily took the "useless" members of the Organization and sent them to their death during 358/2 Days under Xemnas' orders.
In 358/2 Days, Saix seems to care a bit more about Axel then he does in Kingdom Hearts II. He remembers some memories of how Axel and himself used to have a true friendship before they lost their hearts. Then, to contrast his feelings towards Axel, there is Xion who Saix easily calls a puppet and refers to her as an "it" that isn't worth his precious time. Axel and Saix's relationship weakened drastically because Axel was stuck trying to have feelings for Xion and Roxas while Saix was sticking to reality and not getting involved in any sort of emotion. He changed too much after becoming a Nobody, according to Axel, leading to Axel's ignoring him for Roxas and Xion. In Hollow Bastion when Axel and Saix meet again in Kingdom Hearts II, Saix has a whole new outlook on Axel and tells Sora that he is a traitor.
The only true thing that Saix ever seems to "care" about is his heart, memories, and Kingdom Hearts itself. He is very goal-oriented, seen by the fact that he never breaks free from a goal or a commitment that he has made to Xemnas and the idea of Kingdom Hearts. He thinks that he will become "real" if he has a heart, which shows that he is obsessed with the idea of being something rather than nothing. Though all of Organization XIII believes in this, Saix is the most determined to over come it and becomes almost obsessed.
Saix is overall goal-oriented, dedicated, and extremely realistic about his life and the situation he lives in. He doesn't believe in faking who he is or the fact that he can no longer "feel," but he does not let go of his memories of having a heart. Though he uses it for bad sometimes, he is just a character who is in it for himself because he does not feel like he has anyone else that he can rely on for support or help, seeing as though he does not have a heart.