So basically the kingdom hearts equivalent of Dream Zanarkand?
okay to be fair I didn't play KH3 yet, i just got the musician angle from reading the kingdom hearts wikipedia one day. Though that headcanon does remind me of
this image I found on pinterest.
Kairi is a musician. Fits with sora being a pretty good dancer, apparently. She Particularly prefers string instruments.
Kairi is also a Yaoi Fangirl. Conversations tend to awkward between her, Sora, and Riku at times because of this.
The reason Ava didn't come with the other foretellers is that A) she thinks their assholes, *Cough*Fought each other at the drop of a hat when MoM is gone*Cough* and B) she reincarnated a Kairi to guide the Dandylions but got diddlyed in the process and lost her memories until she died at the hands of Xehanort and later revived by Sora. She particularly dislikes Xigbar/Luxu. Her attack known as Foxtrot, where she basically summons a clone army to rekt your ass, ends up being reflected by Xion and Namine, who are kinda clones of her.
The other candidate for Ava reincarnation is Aqua, see also Ven and Foxtrot.
Ventus's Darkness is actually one of the original 13 darknesses of the Original X-Blade due to him being from the original Keyblade War. If it wasn't, then Vanitas would be a regular-ass Emblem Heartless and the Unversed would not be a thing, or at the very least not his Remnant.
If Ventus learns to control this darkness, he can not only make Unversed, but also from Positive Emotions (told apart by the standard flare by their blue eyes and their symbol being colour-inverted). He can't make an army like Vanitas, but hey, quality over quantity. At this stage, he's a "Prince of Darkness".
When he masters this ability and becomes a "King of Darkness", well, let's just say it's a good thing he's a good boi and not nearly as evil as Vanitas. Unversed made at this stage are instead called "Versed".