Senku will be reverting back to his six-year old self. It's a great chance to explore how much more socialized he is now, versus when he was younger. He will be doing exciting things like trying to pry open train doors and windows, and trying to figure out where he is and what he is doing there, and maybe reading. Also, he's on the small side and screams walking target to be picked on, which I am down for. He also doesn't like playing, so good luck with that babysitters. He may also inadvertently explode something. No one needs that toaster right? He can take it apart?

Natsuno is going to stay as he is. He's always been that miserable. It's not that exciting.

Demyx will be a younger, fresh-faced Nobody who's totally not confused about everything and kinda terrified of these other Nobodies who haven't been terribly nice to him since he showed up. I think I've settled on about 14, which is my best guess as to when all that happened. He's not very confident yet and his memories have been put into a blender, so he doesn't really know anything.

Yoite I think I will roll him back a year or so, before his technique-enforced growth spurt, so he's about the size of a nine year old, but really he's 15. He'll have all of his senses back, he's just mute.