It's in human nature to not want to be controlled or told what to do. People are freedom loving, unless you're like Braig who I assume willingly became Xehanort's puppet because he wanted a taste of the power.
There's the thing; what is Vanitas to gain by staying with MX? The X-Blade? He already knows how to forge it. In fact, like you said, he wanted it for his own. Why would he want to share it with MX? Why not betray MX, screw up his plans, and take it for himself and only for himself.
Oh dear, there are enough examples all around of more "subservient" human natures who relish if they can serve either a purpose or another human being/an organisation or a faction. Braig certainly isn't an exception in terms of human behaviour like this, not to mention Nomura mentioning there's still more to Braig's decisions than the current level of information lets us see.
Let's turn the whole thing around: What's Vanitas to gain by betraying MX? Not only would he get another, very powerful enemy in addition to the ones he already has, he also cannot get the X-blade solely on his own anyways. Even leaving aside that he only knows the way how to forge a fraction of the X-blade, he won't ever be successful alone with it since Ventus will never agree with it and try to destroy him again, and Aqua also was "sick of the nonsense" the very first time around.
By going against MX he would be up against MX and his loyal members (at least Ansem SoD, Xemnas, Young MX and Braig) who would probably subdue him very quickly if he tries something
and the Protectors of Light and their allies at the same time.
And I somehow really doubt he would want to ally himself with Maleficent and Pete, lol.
He willingly went against Xehanort's wishes before, when he felt like destroying Ven because that's what he wanted to do. Then Mickey came in and saved him, etc.... So we know that Vanitas doesn't care much what MX wants him to do. Like you said, the only reason he probably worked with MX is because he wanted the X-Blade (IDK about the Keyblade War, I can't really remember him saying anything about that).
Going from the dialogue, it was more like he thought of Ven as useless to their plans since they weren't even in power at that point. Like Ruran pointed out, we don't know if Vanitas even
has any ambitions besides going through with MX's plans and start another Keyblade War.
I've found the quote from the game BBS itself:
BBS said:
Ventus-Vanitas: Correct. I am not Ventus. His heart has become a part of mine
now. This X-blade will open a door--one that leads to all worlds! Then,
Keyblade-bearing warriors will flock here from each and every one of them, to
battle for the light within Kingdom Hearts! And just like the legend says, the
Keyblade War will begin!
Aqua: Shut up! I'm sick of your nonsense! Give Ven his heart back!
That pretty much sums up his motivations as far as we know. There isn't much room to interpret this statement differently.
He wants to see the new Keyblade War unfold, pretty much in line with MX's goals.
If he grows independent enough, which is very possible, he might turn against MX. I wouldn't doubt it. Vanitas wants what Vanitas wants and if there's an easier way to get it, then why not do that? We don't know how easily the Xehanorganization will be able to attain the Princesses, and/or keep control over the more rebellious members.
I see it a lot like Roxas' betrayal; he knew he was being used, so he rebelled and left to get the knowledge and freedom he always sought for. Vanitas is in the same situation, basically, except for wanting power and the X-Blade instead, and thus might do the same.
Though, if Vanitas is fully Xehanortified, then he has no chance unless Sora and the gang find out a way to yank the Xehanort out of people, and somehow feel enough pity to free him. I mean, Sora might take pity on him because it's not entirely Vanitas' fault that he's such a dick; he was born from darkness and negative emotions and was basically raised by MX.
I didn't see anyone specifically denying that it might be a possibility for it to happen, yet there isn't much evidence pointing that way with the current information we have right now.
The point in the scenario you advocate though is that it doesn't get
easier for Vanitas but rather several magnitudes more difficult if he goes against MX to further his own agenda. He would get only more enemies from both sides, not to mention his goals seem to be in line with MX's.
In the case of Roxas it was also that his goals differed greatly with the ones of the people he rebelled against, which isn't the case here as far as we know.
What I do could see though is, if he can exhibit his own will freely and isn't directly controlled by MX and the same goes for Saix/Isa that they may conspire from within the group with their own agenda without openly defying MX.
As for being Xehanortified, we only see Vanitas ever with the golden Xehanort eyes and he was practically alone with MX for four years, so the odds of him being in a tight grip of Xehanort aren't that low.
It depends on what "freeing" him would mean for Sora's group in terms of still being a threat or not. The born from darkness however is a moot excuse since darkness in itself isn't "evil", it's your choices and decisions that decide if you are. It was also not MX who ordered or goaded him into hurting and abusing Ven when he brought him back from Destiny Islands. It were Vanitas' own decisions to act like an sadistic asshole, so much even the very MX had later to interfere and decide to bring Ven to Eraqus.
So if Sora takes pity of not will probably fully dependent on what actions Vanitas takes through the course of future games in the series, and besides, Riku and Naminé also took pity on Roxas and they
still ended his independent existence.
Whether or not Sora and the gang realizes this or completely ignores him and leaves him to be a slave is up to them.
My main fear is that Nomura will make it so Vanitas is just a plain bad guy and has no redeeming qualities. I just want him to have more development in some way, whether it be being more independent, becoming a better person, growing some emotions that aren't dark/negative. Something.
Like I said, it will mainly depend on his own actions and despite Sora being very forgiving in some regards, we also know that Sora doesn't forgive just
anyone. Another thing to keep in mind would be surely also the stances of the rest of "the gang".
Gotta have to agree with that though, in BBS, Vanitas came around as a wasted opportunity because the story never really bothered to invest a bit in his development. In this area, he's in the same predicament as Kairi.
Here comes the tricky part again in that Vanitas over all just plain isn't a very developed character. The only insight we have into Vanitas's and MX relationship besides master and student is in the questionable authenticity of the novels. I couldn't begin to fathom how their dynamic works so for now it can't be said how much Vanitas is unwilling to do what MX says.
Like I said above, yep, it's similar to Kairi, lol.
Vanitas wants the X-Blade and to restart the Keyblade war, but for what reasons is a mystery. He just seems to see the world burn. After the X-Blade is forged and the war restarted Vanitas and MX both get what they want and MX probably wouldn't have any more need for Vanitas. It's a win-win situation for the both of them seeing as they both get what they want so there's no reason for Vanitas to make MX his enemy.
He went against MX's wishes because he reasoned that Ven was more of a hindrance than a help. Ven was a "weakling" while he had Aqua as a spare who was much stronger at the time and potentially more adequate. Looking back at Vanitas's character, everything he did was to speed up his and MX's planes even if it ment taking it into his own hands, but it was still their planes non the less.
To see the world burn, yep, that's what his bragging statements towards Aqua seems to imply.
Again we're on the same wavelength regarding the interpretation of his actions in his first battle with Ven.
imo, the easiest way for Vanitas to get what Vanitas wants is by not pissing off the man who created him and who can probably kick his ass through all the realms in KH. As Sephy pointed out, if Vanitas tries to betray MX, he has MX himself to face and half the new Org. At least.
Lol, exactly. At least by going what we know so far of what Vanitas wants, it is the same thing MX wants in the end.
Vanitas is defiantly being used, and he might know that already, but this goes back to the fact MX and Vanitas have similar goals. Vanitas wants the X-Blade to open KH and restart the Keyblade war. MX wants the X-Blade to restart the Keyblade war. There's no reason why they shouldn't work together. If Vanitas goes off and does his own thing he's going to do what MX wants any way.
That is something I'm curious about though, how much of Vanitas is "Xehanort" by now and how it affects him specifically since he isn't a normal person.
Everyone is used by Xehanort, he knows no "partners" or equals. Other living beings are nothing but tools to him, that is already made abundantly clear also in the way how callously he dismisses the tragedies he caused in BBS. It's no wonder that Mickey is trembling with rage against Xehanort.
Xehanort even uses his
own younger self as a tool in order to try and eliminate Riku. Yep, he even uses
himself.
Exactly, him going off on his own and risk gaining much more enemies only makes sense if his goals would actually differ from MX's.
I think it would probably help a bunch if we could get a glimpse at his ears, lol. Are they pointed? The golden eyes already indicate a vast "Xehanort-contamination" anyways, regardless if his consciousness is still unsuppressed.