Kingdom Hearts is a series well-known in the gaming community for a number of reasons. If there’s one that reaches even outside observers though, it’s the series' often complex and confusing storytelling.
Keeping track of the plot of the series is a mission of its own, not helped by the sheer amount of reveals and plot twists the series likes to employ. With Kingdom Hearts 4 on the horizon, the series is entering a new phase, and instead of trimming down the number of hanging threads, it has opted to increase them. There are tons of secrets being withheld from not just the audience, but even the other characters in the story.
9 Axel/Saix
These two old friends have been on very different journeys since their introduction as part of Organization 13. They share the same spot because they have the same secret. It was known since Kingdom Hearts Birth By Sleep that they had tried to sneak into Ansem The Wise’s castle, but KH3 revealed that they had done so several times, in order to visit a mysterious girl.
This girl is hinted at being a character from KH Union X, most likely Skuld. Whoever she is, Lea and Isa are yet to tell anyone about their relationship with her.
8 Larxene
Despite being a fairly low-ranking villain, Larxene has been one of the most hateful villains in the series. When she was defeated in KH3 she stuck partially to her mean streak but also hinted at a deeper connection between her and another character.
KH Union X has already revealed that she was alive before the keyblade war, but it was assumed that she had lost her memories of that time. With her dying line in KH3 though, it seems like she might remember more than fans are assuming.
7 Demyx
Theories about Demyx and what his true nature is have been around since KH2, first released in 2005. While he’s the resident clown of Organization 13, he’s always had the ability to be very serious when necessary, a fact he spells out in KH3.
It’s possible that Demyx is exactly as he seems, but Nomura is hardly the type to miss out on a good twist. Demyx has a noticeably similar personality to the Master of Masters, leading many to assume he is the master in disguise. This is further supported by the fact that Demyx is one of the few original characters without a proper backstory.
6 Strelitzia
Up until the reveal of Kingdom Hearts 4, fans had assumed Strelitzia was dead. Now that she has been shown to be residing in Quadratum, this brings up a million questions about her whereabouts for most of the series.
As Sora’s apparent new guide, she will likely be quite forthcoming with him in KH4, but considering how KH tends to structure its plot, it’s highly unlikely that Strelitzia reveals all of her secrets from the start. It’s possible that she takes a similar road as Namine and comes clean near the end of KH4, but she might very well reveal herself to be an antagonist to Sora.
5 Xehanort
All throughout the series, Xehanort and his many iterations have been weaving layered schemes behind the scenes. Even after his defeat and death in KH3, the mysteries of Xehanort have only been growing.
He is still the only one who knows the true extent of the experiments he carried out in Ansem’s lab. These experiments likely involved Kairi and other named characters, and there’s also no telling what unused plans he had set up. As KH: Melody of Memory showed, Nomura isn’t quite done with Xehanort yet.
4 Luxu/Xigbar
The reveal of Luxu and Xigbar being the same person is easily the biggest reveal of KH3. It was clear that Luxu was likely still alive in the modern day, but his having been in plain sight the whole time proved just how crafty and unpredictable he could really be.
Now that he’s somehow returned the foretellers to the world, he has a lot of explaining to do on many fronts. How did he bring them back? What other bodies has he stolen? What is inside the box he carries around? Luxu is a cornucopia of mysteries.
3 Luxord
Amongst the ranks of Organization 13, Luxord has always been one of the more mysterious characters. Even after KH3, it’s entirely unclear who he really is or where he came from. However, he now holds a lot of intrigue around him.
His biggest mystery is the function of the card he gave Sora after their fight. He described it as a “trump card,” but what that could mean is anyone’s guess. On top of that, the ending scene from KH3’s Re: Mind DLC shows what sounds like Luxord driving a car in what seems to be the setting for KH4.
2 Yozora
Speaking of KH4, Quadratum is a new setting for the series that has a host of mysteries of its own. It’s spoken of as being a realm of fiction, despite resembling the real world. Yozora seems to be from this realm, but he has so far been very secretive about his exact origins.
The secret boss fight against him gives some hints about his abilities and personality, but it’s entirely quiet on who he really is. He states that his current form isn’t what he really looks like and that he has to save Sora, but is deliberately vague about both these points.
1 Master Of Masters
Of all the characters introduced over KH’s 20-year history, the Master of Masters (aka MOM) is by far the most cryptic, dwarfing even Xehanort in that respect. He’s a bizarrely comedic character despite his apparent power and knowledge and seems to have been the true mastermind of the series so far.
There are only a few living characters who have interacted with him, but even they don’t know what his true plans are. Luxu is the most clued-in, but even he can’t know everything. Honestly, it would be quicker to list the secrets he’s not keeping over the ones he is.