Here's the cast of the prequel, Princess Sapphire's Kingdom Hearts: Birth by Sleep.
- Ventus - Astro Boy (Astro Boy)
- Terra - Professor Ochanomizu (Astro Boy)
- Aqua - Astro Girl (Astro Boy)
- Master Xehanort - Ham Egg (Astro Boy)
- Vanitas - Atlas (Astro Boy)