so can you play mega cd games on a us sega cd?
No, I just use a Japanese system. If you would rather put more work than money into it, you can either hack an ripped iso and change the region, use one of the flash carts (
believe that the Mega Cart and Neo Myth both do import CDs, but I'm not positive), or do both a region mod on your Genesis and a multi or uni-bios mod on your Sega-CD.
I actually have a couple modded Genesis systems and a PAL Mega Drive as well as a multi-bios Euro Mega-CD and it's kinda a pain in the ass flicking two or three switches to play various games (combined with the 2 power supplies). When I do use the modded Mega-CD, I usually just plop in the correct region Genesis/Mega Drive. But I usually play Japanese Mega-CD games on a Multi Mega for convenience.