(SPOILERS) Union X: The ark to the future

[SuperSaiyanSora]

Honestly you're making a better argument for why Ven definitely shouldn't have gotten the BoP then why he should. If the Master of Masters wanted Ventus to play his part in the future Keyblade War he'd need to know as little about his future as possible.

Right, but remember that when we meet Ven in BBS, he was catatonic after what happened with Master Xehanort. Plus, I believe Chirithy mentioned that Ven doesn't remember them anymore. Whatever happened to Ven during the time-span of UX and BBS must've messed with his memory to some degree. So it's possible that even in the memory loss, the MoM knew this was going to happen anyway and was going to choose him because the knowledge would've been the safest with an amnesiac Keyblade wielder. This is a Master who we haven't pinned down truly what his goal is yet, so even though I admit it may be a bit of a stretch, it's not impossible when we know that he's directly manipulated so far already.

Plus, Luxu knew his role for the Keyblade War, was a direct influence, and he body-hopped all this time until now. It could've been the same for Ven had he ended up getting the book.

Also I'm kind of curious, wouldn't the other Foretellers know about the Union Leaders? Luxu certainly did, after all he knew that one of them didn't belong. If the book detailed the events of the future most likely leading up all the way to the clash in KH3, wouldn't there need to be at least a mention on who would lead the unions after them?

Luxu would know because his role was to observe throughout time and watch No Name get bequeathed over and over until the chosen one (Xehanort) would finally try to recreate the Keyblade War. So Luxu would have to know at some point who everyone is, but as far as we know, everyone else died in the War.

But if the book DID have that kind of information, then it would mean that it could be any of the Foretellers that are currently in the shadows manipulating events.

On the point of Ava being the only one to know who the 5 Dandyleaders are, it has been shown constantly that the Foretellers don't have everything as they would have planned. They are constantly found with their pants down about everything going on (especially about the whole "Guilt is the power of Darkness" thing), so I wouldn't be surprised if the information somehow leaked beforehand.

I agree, and it's quite possible that they did know. Of course, we only know so much so I can't say 100% for sure on anything, but it's clear that the Foretellers all had their own agendas. In the Secret Reports, Luxu said that a Darkness threatened the world after they left, so it's implied that everyone besides Luxu weren't present (as far as he knew). Unless Darkness is ALL of the Foretellers, but they just take turns playing the role. (which would be... huh?) But Darkness does have information that most wielders shouldn't, and that's why I'm thinking that their identity has to be of them. Or had the opportunity to explore the tower and read the BoP enough to know what's going on.

...Ava knew that Player knew. Strelitzia going to tell him wouldn't have made any difference which ultimately is the sadly ironic thing about her death. This doesn't make sense as a motive for the murder because Ava had been the one to invite Player, Ephemer and Skuld into the Dandelions. The only way that would make sense is if Ava didn't know who Stre wanted to invite, but even then, as a Dandeleader part of her job was to recruit more Dandelions, so unless she had to tell that she was a leader (which I don't think she was going to as there would be no reason to mention that), I don't see a reason to kill her for that.

You make a good point. But then, maybe Strelitzia WAS going to mention she's a Leader. She had her rulebook and we know that she wanted to talk to Player, but in her desperation... Who knows what she would've said. Honestly, I typed up the theory of Strelitzia being silenced, but I can admit that I'm taking a lot of leaps on this one. That's why I think we don't have enough information, but the basis for the theory is moreso off the idea that if Ava = Darkness, what if Darkness was responsible for killing Strelitzia? This is ALSO based off me wondering if the False Leader and Strelitzia's Murderer are the same.

Cause let's say Ven isn't a chosen leader after all, it may not be set in stone that he killed her either (although the logic is there). If the False Leader and Killer aren't the same, then how did the F.L. get the Rulebook? It would've had to have been given by someone respectable, someone everyone knows that they were in charge of organizing the Dandelions -- Ava.

Occam's Razor would be, False Leader = Killer, but neither Union member has shown the propensity as of right now to murder someone in cold blood, in the back of a house in pitch black darkness. It doesn't mean it's impossible, but then someone right now would have to be lying about their very nature. Who that would be... I guess Brain is suspecting either Ven or Skuld.

The replacement would know because presumably they were told after Stre died. Stre died right after the bell rung signifying the Keyblade War, and that means that they would have been given their book right before it as well, because we see her assassin take her book.

To be fair though, I thought about it a bit and realized that it was just that I've projected my knowledge of Stre being a Dandeleader onto the cast, as only Brain and Ephemer know now that she was supposed to be one of them. So only after one they gather everyone up can they spread that info. Darn it, it starting to look like Laurium is his sister's replacement. Its just a feeling but a bad one to be sure.

Also Crackpot theory time:

MoM said that in his time, Darkness took the shape of people, and it was a mess telling friend from foe, so what if one of our current cast is actually not just an unwilling vessel for darkness, but darkness is their true nature?

Whoever killed her, knew about the book. That much is for sure. But who it is, I honestly don't have a clue. For all intents and purposes, Strelitzia dying doesn't make sense, because how did anyone know SHE had a rulebook? That's why I'm thinking it would've had to have been someone privy to the knowledge of the next Union Leaders. The Master of Masters knew obviously because he chose them, Ava knew because it was her role... So who else? Unless Luxu was listening in on the whole conversation and decided to kill Strelitzia for whatever reason, but then why? Or, if the Foretellers knew about the next chosen five, what motive would any of them have for killing Strelitzia?

If the False Leader is the killer, it makes things easier, but I just can't help but wonder how they would've known to go after her. As far as anyone else was concerned, she was a regular Dandelion. Nobody was supposed to know who was a leader and who wasn't. Unless she was stalked, but then, why?

Regarding the theory, it's possible, but then that would mean it would either be Ven or Skuld. Ven because of Vanitas and Missing Ache, and Skuld because... We don't don't really know all that much about her. MoM is also very cryptic, so who knows what he's saying when he talks about this.

 

[AdrianXXII]

Right, but remember that when we meet Ven in BBS, he was catatonic after what happened with Master Xehanort. Plus, I believe Chirithy mentioned that Ven doesn't remember them anymore. Whatever happened to Ven during the time-span of UX and BBS must've messed with his memory to some degree. So it's possible that even in the memory loss, the MoM knew this was going to happen anyway and was going to choose him because the knowledge would've been the safest with an amnesiac Keyblade wielder. This is a Master who we haven't pinned down truly what his goal is yet, so even though I admit it may be a bit of a stretch, it's not impossible when we know that he's directly manipulated so far already.

Plus, Luxu knew his role for the Keyblade War, was a direct influence, and he body-hopped all this time until now. It could've been the same for Ven had he ended up getting the book.

It's possible but I don't see the advantage in giving Ven, who's the youngest of them and still rather shy and not very confident a book detailing the hardships he'd have to endure in the future.

We still don't know exactly how Ven, Lauriam, Elrena and the others get to the future. KH3 strongly implies what ever helped did wipe their memory. I do find it interesting that out of the 5 union leaders at least 2 maybe 3 ended up displaced in time.
This does support that MoM planned on them to end up in the future. I mean why else put them in a position that'd make them more likely to get involved with the Ark.

I do find it interesting what ever brought them to the future took them to roughly 15 years before the Keyblade War would occur. Wonder if there's some event that took place at that point in time leading them to be scattered, though I guess everyone besides Ven could have also just randomly appeared within the time range of Sora's birth and Roxas' creation.

Luxu would know because his role was to observe throughout time and watch No Name get bequeathed over and over until the chosen one (Xehanort) would finally try to recreate the Keyblade War. So Luxu would have to know at some point who everyone is, but as far as we know, everyone else died in the War.

But if the book DID have that kind of information, then it would mean that it could be any of the Foretellers that are currently in the shadows manipulating events.

Honestly we don't know what happened to the Foretellers, if they died or if they just dimmed and faded like the Master of Masters. For all we know they could have taken arks of their own to the future.

We also don't know how Demyx and Luxord's original selves were involved. They'd somehow have to end up where the time travel shenanigans happen. I guess one of them could be Darkness acting as an agent for one of the Foretellers or even MoM himself.

If the False Leader is the killer, it makes things easier, but I just can't help but wonder how they would've known to go after her. As far as anyone else was concerned, she was a regular Dandelion. Nobody was supposed to know who was a leader and who wasn't. Unless she was stalked, but then, why?

Regarding the theory, it's possible, but then that would mean it would either be Ven or Skuld. Ven because of Vanitas and Missing Ache, and Skuld because... We don't don't really know all that much about her. MoM is also very cryptic, so who knows what he's saying when he talks about this.

The Fake Leader being the killer would make things simpler, but at the moment none of them really seem like people who'd do such a thing.

Besides it's not hard to imagine Darkness or the Nightmare Chirithy lurking in the shadows following Ava's every move to know what the MoM was planning. I mean others had noticed that she was talking across unions recruiting Dandelion, so if someone was plotting against them, following her would make sense.

 

[SuperSaiyanSora]

It's possible but I don't see the advantage in giving Ven, who's the youngest of them and still rather shy and not very confident a book detailing the hardships he'd have to endure in the future.

We still don't know exactly how Ven, Lauriam, Elrena and the others get to the future. KH3 strongly implies what ever helped did wipe their memory. I do find it interesting that out of the 5 union leaders at least 2 maybe 3 ended up displaced in time.
This does support that MoM planned on them to end up in the future. I mean why else put them in a position that'd make them more likely to get involved with the Ark.

I do find it interesting what ever brought them to the future took them to roughly 15 years before the Keyblade War would occur. Wonder if there's some event that took place at that point in time leading them to be scattered, though I guess everyone besides Ven could have also just randomly appeared within the time range of Sora's birth and Roxas' creation.

I feel like out of everyone we know, the best person to have the Book of Prophecies would either be Ephemer or Brain (who currently already has it and was chosen by Ava). But then again, we also don't know what the Master's end game is. He says he wants to put an end to the Keyblade War, but what's really going on? He hasn't told anyone what the rhyme or reason behind any of this is, not even Luxu fully knows what's going on and the Master probably confided in him the most (for whatever reason).

Honestly we don't know what happened to the Foretellers, if they died or if they just dimmed and faded like the Master of Masters. For all we know they could have taken arks of their own to the future.

We also don't know how Demyx and Luxord's original selves were involved. They'd somehow have to end up where the time travel shenanigans happen. I guess one of them could be Darkness acting as an agent for one of the Foretellers or even MoM himself.

Well, we know at the end of KH3, Luxu summoned every Foreteller except for Ava back. Prior to this, we know they fought in the war. So you're right, we really don't know what could've happened during that time. It's implied that they were all dead. But then it's also interesting because if they were dead, how did Luxu gain the power to bring people back from the dead? I don't think we've ever really asked this question, and they all just walk out of a portal like nothing happened?

Luxord and Demyx seem to be the two most mysterious characters in ReMIND so their roles have to be pretty big in all of this. Certainly big enough for them to be in present day, for whatever reason.

The Fake Leader being the killer would make things simpler, but at the moment none of them really seem like people who'd do such a thing.

Besides it's not hard to imagine Darkness or the Nightmare Chirithy lurking in the shadows following Ava's every move to know what the MoM was planning. I mean others had noticed that she was talking across unions recruiting Dandelion, so if someone was plotting against them, following her would make sense.

Right, so that's why I'm not sure if the Fake Leader and the killer are one in the same. Of course, it's definitely possible for someone to be completely hiding their true nature, but... What's the goal?

But if it IS Ventus (which, hoo boy), it might explain how the Master of Masters mentioned that during the Keyblade War as a kid, he fought against beings that "weren't human"... Because Vanitas wasn't human, and it's strange how one Keyblade wielder who was stripped from the heart of their true self is able to create a completely new type of monster that is not only born from negative emotion, but they also return to said individual once defeated. This is extremely strange, and because of Vanitas, we never see the Unversed again until in KH3, and it's the only world he reappears in (that we can visit). Vanitas is Ven's darkness given sentience, so maybe Nomura may come out and say "Oh yeah, Ven isn't exactly human either."

Maybe we'll also get an explanation for Vanitas's outfit and why it's similar to Riku's in KH1 (and by an extension, Repliku's). In fact, we already know that Vanitas's face is because of the events in BBS. But in terms of his outfit (especially his helmet), it was never explained, I feel like maybe there's a bigger reason for it. It could be just a "dark suit", but I'm not convinced.

 

[Deleted member 252753]

Vanitas is Ven's darkness given sentience, so maybe Nomura may come out and say "Oh yeah, Ven isn't exactly human either."

Another who may not be exactly human is Subject X (assumedly Skuld). In her secret report she says she does not understand 'Who or what" she is and even asks "Am I alive?"

 

[ZeVaine]

If the Vanitas theory is true, then how does Ven/Vanitas have access to the BoP?

Someone is either manipulating that side of him, or at least cooperating with the Vanitas side of him.

 

[AdrianXXII]

I feel like out of everyone we know, the best person to have the Book of Prophecies would either be Ephemer or Brain (who currently already has it and was chosen by Ava). But then again, we also don't know what the Master's end game is. He says he wants to put an end to the Keyblade War, but what's really going on? He hasn't told anyone what the rhyme or reason behind any of this is, not even Luxu fully knows what's going on and the Master probably confided in him the most (for whatever reason).

Yeah, Ephemer is definitely my primary candidate for who actually should have gotten the book. He just seems like the natural leader and would be responsible enough to entrust with it.

The Master's plans are a mystery as are his true goals. His method seems to lead to a lot of strive and conflict though. Well at least leading up to Union X.

Well, we know at the end of KH3, Luxu summoned every Foreteller except for Ava back. Prior to this, we know they fought in the war. So you're right, we really don't know what could've happened during that time. It's implied that they were all dead. But then it's also interesting because if they were dead, how did Luxu gain the power to bring people back from the dead? I don't think we've ever really asked this question, and they all just walk out of a portal like nothing happened?

Luxord and Demyx seem to be the two most mysterious characters in ReMIND so their roles have to be pretty big in all of this. Certainly big enough for them to be in present day, for whatever reason.

Well apparently he called all of them just Ava didn't answer his summon, either because she didn't want to or because she couldn't thanks to the actions she took not placing her where she should have been to be summoned.

Yeah seems like Re:Mind will at least try and shine some more light on those two. Though at them moment I wouldn't be surprised, if it weren't just more foreshadowing with UX being left to actually elaborate on them, though I don't think it'll be this season.

Right, so that's why I'm not sure if the Fake Leader and the killer are one in the same. Of course, it's definitely possible for someone to be completely hiding their true nature, but... What's the goal?

In most mystery stories there'd be cracks and clues for the viewer to pick up on. While I have't been really observant I can't say I personally noticed any. I find Darkness being a 6th player in the whole thing and having killed Strelitzia and tricked someone to take her place could work, with what we have so far. At the moment I'd prefer it even.

But if it IS Ventus (which, hoo boy), it might explain how the Master of Masters mentioned that during the Keyblade War as a kid, he fought against beings that "weren't human"... Because Vanitas wasn't human, and it's strange how one Keyblade wielder who was stripped from the heart of their true self is able to create a completely new type of monster that is not only born from negative emotion, but they also return to said individual once defeated. This is extremely strange, and because of Vanitas, we never see the Unversed again until in KH3, and it's the only world he reappears in (that we can visit). Vanitas is Ven's darkness given sentience, so maybe Nomura may come out and say "Oh yeah, Ven isn't exactly human either."

I feel the explanation of what and who Vanitas is works with what we have been given so far. I assume that when he was created he also absorbed darkness from around him, leading to him being stronger.

I'd personally prefer for Ven to just be a 12 year old kid over his head in this part of the MoMs plans. Him not being human would also effect Sora, seeing those two are deeply connected, and him being responsible for a death and other evil deeds would make him less likable and require damage control later on.

On top of that, if Ven had that kind of Darkness than Xehanort wouldn't have talked about him the way he did in his reports and could have used him as a vessel no problem.

 

[Deleted member 252753]

On top of that, if Ven had that kind of Darkness than Xehanort wouldn't have talked about him the way he did in his reports and could

Well the BBS reports aren't totally consistent on that. On one hand Xehanort does say that Ventus was too 'benign for his own good' but then says that Ventus was 'too frail' to serve as a vessel, suggesting physical weakness, not lack of darkness was the problem.

And then of course the reports go onto explain that Vanitas 'took too much of Ventus's heart', nearly killing the remaining light, which needed to be strengthened to match Vanitas' darkness.

This suggests that actually darkness was dominant in Ventus's heart before the split

 

[Sora’s Skyline]

Well the BBS reports aren't totally consistent on that. On one hand Xehanort does say that Ventus was too 'benign for his own good' but then says that Ventus was 'too frail' to serve as a vessel, suggesting physical weakness, not lack of darkness was the problem.

And then of course the reports go onto explain that Vanitas 'took too much of Ventus's heart', nearly killing the remaining light, which needed to be strengthened to match Vanitas' darkness.

This suggests that actually darkness was dominant in Ventus's heart before the split

but when we see the “circle” of Ven at his SOA we see it’s about 60-40, 60% there and 40% gone, meaning to me he is 60% light, then his heart merges with Sora’s to recomplete the circle.

So basically inconsistencies everywhere

 

[Ballad of Caius]

I get where everyone is coming about Vanitas being a lot of darkness, but why is everyone assuming that Vanitas was organically born like that? For all we know, Master Xehanort must have meddled some way in order to properly create an opposing force to Ventus' pure light..

 

[Violet Pluto]

but when we see the “circle” of Ven at his SOA we see it’s about 60-40, 60% there and 40% gone, meaning to me he is 60% light, then his heart merges with Sora’s to recomplete the circle.

So basically inconsistencies ever

Isn't that at the end of the game though, where it is noted that Ventus has become strong enough to finally stand against Vanitas? It could be that when they say that, he was steadily repairing his heart while it was connected with Sora's and so, when it is broken again, it isn't as bad as it could have been, seeing as he didn't just die. I would posit that Vanitas was more of the heart (or more powerful) than Ventus, because Vanitas, after he was created, got up and walked away. Ventus was catatonic for a very long time, and that was with Sora's heart supporting him. Why is Vanitas so powerful, not just when terrorizing the worlds, but also when first created, to the point where Ventus would have died from his absence, but he wouldn't from Ventus'.

 

[Any]

I get where everyone is coming about Vanitas being a lot of darkness, but why is everyone assuming that Vanitas was organically born like that? For all we know, Master Xehanort must have meddled some way in order to properly create an opposing force to Ventus' pure light..

I think it’s because Vanitas said his heart was incomplete when he confronted Sora, right? Assumption but if Xehanort nurtured Vanitas heart, I don’t think he would complain about his heart being incomplete. I think Xehanort just trained Vanitas to become stronger and nothing else. Unless he was talking about the state of his heart being incomplete due to the X-blade shattering his heart.


I’m surprised no one brought up void gear having two of MoM’s eyes lmao.

 

[AdrianXXII]

I get where everyone is coming about Vanitas being a lot of darkness, but why is everyone assuming that Vanitas was organically born like that? For all we know, Master Xehanort must have meddled some way in order to properly create an opposing force to Ventus' pure light..

Yeah, I agree it seem like Xehanort did something to strengthen the darkness inside of Ven, to make it stronger and more likely to stand up to Ven's light. Not considering he might have to do something to reinforce Ven's hurt heart of light.

There was a lot of darkness swirling into the part of the heart that would became Vanitas. Potentially from the Heartless Xehanort had previously summoned?

Also looking at Ven's Station of Awakening I'd say Vanitas made up at most 30% of Ven's heart probably closer to 25% or less seeing Ven did mention what he has left was slowly slipping away as well. Which I took as his heart eroding.



This amount of darkness in someone's heart would seem normal to me. Besides in UX there are no real signs of Ven having a lot of darkness in him, he's neither angry, greedy or depressed, which would be obvious tells of darkness. Though who know's he might be deceitful.

 

[yuyayuzu]

You know, I just though of something strange. We are under the assumption that only the fake leader that is the one is responsible for Strelitizia's death whether it is intentional or not. But isn't there a possibility that one of the chosen union leader works together with the fake one ? It seems too far-fetched and I know other union leaders aren't supposed to know who are the other leaders before meeting them in person but hmm.. I just imagined something like this
- Someone tells the chosen leader the other supposed-to-be-chosen leaders
- That someone strikes down Strelitizia
- The fake leader replaces Strelitizia.
- The fake leader and one chosen leader secretly works together
Okay, maybe impossible. I just remembered that most of the time Ven is together with Skuld so it feels quite strange since I think Skuld is supposed to have more screen time with Ephemer

 

[Deleted member 252753]

Thinking about it, what I don't buy is the idea that Xehanort could have split any keyblade wielder's heart in two and that it being Ventus/Vanitas is just a coincidence. Even in BBS, Xehanort says he felt he was 'destined' to meet Ventus and I think the creation of Vanitas was an important moment in someone's plan, be it the MoM or Darkness.

Watching Ventus's conversation when he meets Ephemer and Skuld in the KG reinforces this in my view. Ventus wonders why he was chosen as a leader because there is nothing special about him, which makes me think he is actually very special and important in some way. I would bet the farm on him either being the imposter or the intended recipient of the BoP.

In this conversation Ventus also states that he is jealous of Ephemer and Skuld's friendship, because he has always been a loner. This reminds me of Toy Box, where Young Xehanort links darkness and loneliness ("If the light of friendship is a form of power, then the darkness of being alone is a power even greater"). YX also talks about doubt allowing the darkness to enter someone's heart too so we see that Ventus is at least susceptible to darkness, even at the start.

My guess is the Darkness killed Strelitzia and disguised itself as Ava to make him a union leader (Ventus makes clear he didn't know Ava well, suggesting he could be fooled by the disguise). The Darkness, whatever it's origin, could eventually enter Ven's heart to go with him to the future where it would be brought out by Xehanort as Vanitas.

 

[Sign]

You know, I just though of something strange. We are under the assumption that only the fake leader that is the one is responsible for Strelitizia's death whether it is intentional or not.

Not really. There are some people who believe this but being the murderer and the imposter are not exclusive to one another.

It seems too far-fetched and I know other union leaders aren't supposed to know who are the other leaders before meeting them in person but hmm.. I just imagined something like this
- Someone tells the chosen leader the other supposed-to-be-chosen leaders
- That someone strikes down Strelitizia
- The fake leader replaces Strelitizia.
- The fake leader and one chosen leader secretly works together

Yeah, it is farfetched lol. It's not impossible of course, but there's no evidence of such a thing happening at this time.

Okay, maybe impossible. I just remembered that most of the time Ven is together with Skuld so it feels quite strange since I think Skuld is supposed to have more screen time with Ephemer

Skuld has never had more screentime than Ephemer. I love the girl but she is poorly developed with little to no agency of her own. Even at her most active, her character revolved around one of three things: Ephemer, Player or her duty as a Dandelion.

 

[Kokoko253]

My guess is the Darkness killed Strelitzia and disguised itself as Ava to make him a union leader (Ventus makes clear he didn't know Ava well, suggesting he could be fooled by the disguise). The Darkness, whatever it's origin, could eventually enter Ven's heart to go with him to the future where it would be brought out by Xehanort as Vanitas.

I love this idea! Darkness' goal could be to get to the future, maybe even to chase after MoM. It knows that the Union Leaders (and Elrena and Luxord and Demyx's somebodies) will be brought to the future, so kills a Leader, and puts in her place a guy he possesses, who's 'darkness' will be extracted and given shape later.
So, basically the Reverse Vanitas Theory, instead of Vanitas going back to the past and becoming Darkness, it's Darkness going to the future to become Vanitas. My only problem is that Vanitas gives off no signs of being someone else other than Ventus' darkness. He was empty when he was born.
But traveling to the future being Darknesses goal is something I can belive.

 

[Sephiroth0812]

I just remembered that in the original Chi when Ephemer goes to the Foreteller's tower alone after parting with Player he meets a figure in a black coat.

Back then we always theorized it being either MoM or Luxu, but now...could that have been Darkness investigating the tower by themselves?

 

[Twilight Lumiair]

I just remembered that in the original Chi when Ephemer goes to the Foreteller's tower alone after parting with Player he meets a figure in a black coat.

Back then we always theorized it being either MoM or Luxu, but now...could that have been Darkness investigating the tower by themselves?

Actually, I believe the general consensus for who the shrouded figure in that scene was, is Ava. It was presumably the moment she first contacted him about leading the Dandelions, and they relocated to the cliffside we see Ephemer receive the rule book at later on. The KHwiki even supports this idea.

I kind of always took it as a sign that Ava could very well be darkness, since she would've had precedent for appearing that way before. But I guess in the end, we still don't know for sure.

 

[Chainofmemories]

It would be a very nice plot twist if Darkness turns out to be Strelitzia in some way, like her ghost or nobody.

 

[Deleted member 252753]

I love this idea! Darkness' goal could be to get to the future, maybe even to chase after MoM. It knows that the Union Leaders (and Elrena and Luxord and Demyx's somebodies) will be brought to the future, so kills a Leader, and puts in her place a guy he possesses, who's 'darkness' will be extracted and given shape later.
So, basically the Reverse Vanitas Theory, instead of Vanitas going back to the past and becoming Darkness, it's Darkness going to the future to become Vanitas. My only problem is that Vanitas gives off no signs of being someone else other than Ventus' darkness. He was empty when he was born.
But traveling to the future being Darknesses goal is something I can belive.

I would agree that's a problem with the Vanitas theory but of course if the Darkness did travel to the future inside someone it would have other candidates too.

A reason Vanitas could seem to just be Ven's darkness and a blank slate is that he too is affected by amnesia so wouldn't know his own nature. Part of the Darkness's plan could have even be to position itself so its memory would eventually be restored somehow and its true nature revealed.

Ven's Chirithy in the Final World does seem uneasy about his master's memories being restored, saying 'he's probably happier with his new friends'. To me, this doesn't necessarily mean Ven was evil but that his memories at least include sadness of some kind.

Thinking about it, this amnesia thing could point to Skuld, looking at the Secret Reports about Subject X. We know that the amnesiac (Terra-)Xehanort wanted to unlock her memory with his experiments but she was hidden from him and he was forced to experiment on himself instead, unlocking his own memory and his darkness.

And Subject X's own report suggests that it was Braig who hid her from Xehanort. If so, this would be the first time we know of when Braig/Luxu acted against Xehanort's wishes. This could be because Luxu has identified Skuld as the virus in the MoM's plan and unlocking her memory would derail the plan further.

One more thing about Vanitas, though. He has been shown to be something a little more than Ventus's darkness. He also formed a connection to another heart, through Ventus who now defines him in the same way that Ventus does, according to final words in the KG. I find it difficult to believe the connection of this being of pure darkness to Sora is insignificant.