i have a new theory to tell. Well the next game is not going to be called kh3, but is going to be called Kingdom Hearts why because if you remember the kh:final mix trailer it says at the end Kingdom Hearts 2 ,but for the Kh2:fm trailer at the end it said Kingdom Hearts.
The B.H.S Soldier name is probably Ven because when you battle the E.S soldier he says Aqua.....Ven
which is probably refering to the other two soldiers probably. The possible reason why he looks like roxas
is maybe he is soras brother or some other type of relation or even a rei9ncarnation.
The F.S Soldier looks a lot like Kairi and her name is Aqua the fact behind this is guess is the same as the B.H.S one. I don't have a lot of information on who she might be or what she is related to the series.
The E.S is for sure not Xehanort because in KH2:FM if you beat him and you come back to battle him again he says , You have returned young keyblade master i have nothing to give.but my hatred towards Xehanort
he also has a changing eye affect like Xehnort,but he is not him. Maybe he had gotten some of Xehanort trates some how or he had gotten some of his power like riku. And his eye changing event occurs when he gets angry.
As for the bald dude he is the true form of Xehanort because he is a keyblade master like him and if you've noticed his eyes are yellow just like Xehanort when he interrupts Ansem the wise in Hollow Bastion
he also is interested in Kingdom Hearts just like Ansem and Xemnas to explain his memory lost he had probably gotten beaten by the some other keyblade masters ( not the three in the tralier) and after he raigained he had come to get his revenge on the keyblade masters of nowadays so he revels his true form since he was beaten in his original form. As for the soldier next to him is his form he had used in the old battle he had summoned it to help him now.
As for mickey he is using the star seeker keyblade which means he had finished his training with YenSid which means it happened right after the ending of KH2 which also explains the letter given by Mickey to Sora and the gang they seem worried near the end.
