The “Kingdom Hearts Premium Theatre Event” will be held twice on December 3, 2015 and will be a talk-show event featuring special guests and never-before-seen footage of Kingdom Hearts III.
Ticket purchases are separate from admission to D23, and will be available in a raffle event from September 15 – 24 for 1,500 yen per ticket. Winners will be announced September 29. Check out the link for a chance to get tickets — a Disney Japan account is required.
Disney announced earlier this week that Kingdom Hearts III will feature a Big Hero 6 world, taking place after the events of the film.