I picked up an odd Mega Drive game at the Goodwill last weekend.
The game is Sunsoft's 1990 Batman based on the movie.
The intro text is in English but what I find odd is that the game comes in a hard plastic case that is just a little bigger than the cartridge and includes a tab for holding maybe a small instruction book. Plus the case opens and is labeled to open the opposite direction of the US Genesis case.
The PCB (is that what it's called) is clearly marked with Sunsoft as is the rom chip and the warning label on the back of the cartidge is in Japanese.
It plays perfectly fine on my Nomad.
I'll try and post pics soon.