AIO stands for all in one. That should help a lot. Honestly, I recommend starting with the localized version. It's a bit rough, but you have plenty of content and 3(4 today if you can get your hands on the new DLC) personalities to try out. Naturally this version is way behind in content.
That's all in a reasonable, ahem, download size as well and you can figure out if you actually like the game. Once you get how it works and want more content, got for the com3d2 JP version that has more than double the content, which you can even update with the old content from cm3d2(the older, separate, game). The machine translation is meh, but technology has come so far that it is semi coherent that you can imagine the basic premise.
The JP download sizes can reach 60-75 GB each, hence why taking the plunge and the hassle of getting it to work with mods and stuff is such a pain. The AIO downloads are therefore a godsend in getting them to work easily. Good luck.