Oriental Blue: Ao no Tengai for the Gameboy Advance is so far off from the previous games that you wouldn't even think it was a Tengai Makyō game if it weren't for the fact that it was designed by Red. While it still starts off in ancient Japan, this game plays it entirely straight, even abandoning the bright anime character designs for a more serious look. Despite the drastic change in tone, once you play the game, it's pretty clear this is a successor to the "Far East of Eden" series.
A version of this game was originally in development for the short-lived Nintendo 64DD before being quietly canceled due to the hardware's discontinuation. Hudson has never shown any official images from this build, but it would have probably looked like the GameCube remake of Tengai Makyō II: Manji Maru with 3D low-poly environments and sprite based characters. The project was resurrected and re-developed as a Gameboy Advance game and finally released in 2003.