There is only one way this scene works from a perspective standpoint:
Vanitas is definitely in the Land of Departure’s throne room.
But the decor on the archway is at the very top and the only way it works is if Vanitas is perched on top of the throne Ventus is sitting in. Like so:
Or he’s standing up, but he’s leaning on something so I assume his own knee.
Whoever he’s talking to is right in front and he’s looking down at them. This is definitely during Ventus’ awakening and they are gonna have a rude visitor.
tbh whenever i see speculation in the kh fandom about whether or not vanitas is gonna be in kh3 and if so what side will he be on in the inevitable clash with xehanort and will he get a redemption arc or not all i think about is how i can’t imagine things with vanitas playing out any other way than
Plot Designing 