∞;4122827 said:
So they're secretly good guys, in a way?
We actually don't know who they really are in their original selves (We know that they're best friends in the past but who are they really?) , apart from the first six members who are the apprentices of Ansem the Wise who would become the founders of Organization XIII.
I speculate that during when they are in their original persona, I got the feeling that they met the three keyblade masters in their world and heard that they said about searching Master Xehanort who is looking for the seven hearts of the princesses of light to open the door to darkness, Kingdom Hearts.
It could be possible that Axel's and Saix's original selves would learned of this and wanted to free the hearts from the door but their plan failed when their world is destroyed. The result turns them into Nobodies, but they retained their memories of their original selves and still continue to achieve their plan.
My second speculation is that they themselves came from a group of people who know something about the Unbirths and learn about the darkness threatening their world, would form a group that their purpose is to free the hearts of the people that are lost to the darkness, and sent to the door of darkness, Kingdom Hearts but their plan failed when their world is destroyed by an unknown force which is later revealed to be caused by the Heartless and during that event, Saix's face was scarred as a result. During their time as Nobodies, Saix told Axel to achieve their plan and says the latter's real name, which Axel looks disappointed and walk away. (Possibly because his best friend still going on with their plan but he had changed now, as a Nobody or another fact that Axel remembers the good times that they both hang out together in the past but can't seem to forget it).
I once did a theory about Saix original self few years ago after the releases of KH2 (it was before we know that Axel used to Saix's best friend in the past) in which Saix had a loved one, his fiancee who always stand by his side and they always look at the moon during night time until the Heartless destroy the world. Saix became a Nobody and became emotionless due to the event happen to his loved one. He would look at the moon at the WTNW, which reminds him of the time he and his fiancee looks every night, and determine to get his heart back to become original and possibly his loved one's heart from KH.