Kingdom Hearts May Have Just Uncovered the Mystery Around The Darkness

Fans of the long running Kingdom Hearts series should be well aware by this point that the primary antagonist of the series is the ever looming presence of darkness, who may have even controlled Xehanort's past. What some fans may not be aware of, at least if they haven't been meticulously following the mobile title Kingdom Hearts Union X, which has undergone a number of name changes in the past, is that the Darkness has a capital 'D' now.
That's right, taking a note from Destiny 2's mysterious 'Pyramids in Space' ending, Kingdom Hearts has recently personified the Darkness, with a figure shrouded in shadow who interferes with the worlds. However, thanks to some new dialogue from the latest update of Kingdom Hearts Union X and the recent Kingdom Hearts 3 Re:Mind's hidden details, there may be new evidence to who this Darkness character is and who the true villain of the series really is.

Who is the Darkness?

To begin, let's look at who this Darkness character is and what he's done so far. While it isn't explicitly explained in the game, Darkness seems to first appear at the end of Kingdom Hearts X, the original Japanese mobile title, where he kills a character named Strelitzia. The exact identity of Strelitzia is less important for now, but what is important is that she was chosen to be a new Union Leader after the Keyblade War destroyed the world and has led to every game in the Kingdom Hearts series.
After killing Strelitzia and stealing her rule book that was supposed to guide her as a new Union Leader, the Darkness moves on to interact with Maleficent who has traveled back in time, like Xehanort does in his past, for reasons to complicated to get into right now. So far though, the last we've seen of the Darkness is him leading Maleficent to a time travel device that for the sake of convenience we'll call The Ark. Supposedly, this Ark is incomplete and will only allow Maleficent's heart to travel back to her time, but the Darkness needs her to travel forward to be an anchor for others to follow.

Ventus in the Past

One of the biggest surprises from Kingdom Hearts Union X was that Ventus from Birth by Sleep appeared to be from the time of the ancient Keyblade War, suffering again from amnesia. After the events of the Keyblade War, Ventus appeared and claimed that he was told to be one of the new Union Leaders, carrying a rule book as proof. Recently, it's been revealed that Ventus was never chosen to be a Union Leader, and instead he has Strelitzia's rule book and has seemed to unknowingly taken her place as well.
This revelation came from the character Blaine, who has been assumed up until this point to be the secret villain, due to his mysterious appearance along with his dark character design. However, with the reveal, many of the other characters seem to assume that Ventus wasn't aware of not originally being chosen to be a Union Leader and assumed that the discrepancy is linked to his amnesia, likely because Square wouldn't want to turn a fan-favorite Kingdom Hearts playable character into a villain. Ventus' presence in the past has also been confirmed at the end of Kingdom Hearts 3 when the Chirithy, who only previously existed in Union X, from the Final World is shown to be bonded to Ventus.

The Darkness in Ventus

One important thing to note about the Darkness is that, as the character interacts with Maleficent, it seems as though it can't physically interact with the world on its own. Instead, it needs to inhabit a body in order to take any physical actions, like killing Strelizia. Considering that Ventus is the one who gets Strelizia's rule book and has some issues with memory, its more than likely that the Darkness has been inhabiting the boy in order to enact the mysterious, dark plans, which could direct Kingdom Hearts 4 and other future games.
This goes fairly well in line with what we learn of Ventus later in the series, but more on that and other retcons later. For now, the important note is that the clues all point to the Darkness periodically possessing Ventus. It's likely that Ventus continues to be the vessel for the Darkness in the future as well, and of course that means far into the future, as in Birth by Sleep era, which hopefully means we may get more answers in Kingdom Hearts Dark Road.

The Ark

The time traveling Ark that the Darkness leads Maleficent to is something that many players may have recognized from the very first Kingdom Hearts title. It appears in the final level, End of the World, as a sort of recreation that Sora has to travel through on his path to confront Ansem. Most players assumed at the time that this area was an unexplored section of Hollow Bastion, due in part to the architecture falling in line with the previous level with sharp edges and brass pipes everywhere. However, it seems that this area is really The Ark from Daybreak Town, although it may still be connected in some way to Hollow Bastion, or Radiant Garden.
Although, one major difference between Union X's Ark and Kingdom Hearts' Ark is that the original only showed five pods, but the new version shows seven. That might be explained at some point, but regardless, this device is the explanation players needed to understand how Ventus shows up in the Birth by Sleep era, again with no memories, along with Marluxia/Lauriam and Larxene/Elrena. Needless to say, the future of Kingdom Hearts relies fairly heavily on who used these pods, although the process isn't exactly prefect thanks to the user being stripped of their body and only traveling as a heart.

Vanitus

Going over another origin story one more time, Vanitus comes from Birth by Sleep and is the considered to be the dark part of Ventus' heart that Xehanort freed when experimenting with the X-blade. That has been the story since Birth by Sleep, but a new scene in Re:Mind has changed that backstory a bit. In the scene, Vanitus claims that the "dark part of Ventus' heart" bit wasn't entirely true, and instead he is a separate dark entity that has been with Ventus for a long time.
So, Vanitus is a dark entity that has been with Ventus for a long time, that literally refers to itself as "The Darkness" right before disappearing after the fight against him at the end of Kingdom Hearts 3. And this is where Union X has made sure to solidify its place in the lore of the Kingdom Hearts series. Considering how the Darkness seems to be working against the Master of Masters, it's possible that this character, and therefore Vanitus, may be the true villain of the continuing series.

Bonus: Sora's Nightmare

As a bonus, Sora's Nightmare from Dream Drop Distance could be connected to the Vanitas/Darkness entity as well. A mysterious, dark figure appears in one of the dark Organization hoods, but there is little explanation for where this comes from. However, this does happen while Ventus is still recovering inside of Sora's heart, making him another vessel for the Darkness, which is likely what the Nightmare represents. And for anyone who's still lost, players can catch up on the Kingdom Heart series on PS4 and Xbox One now.