Welcome back co/m/rades,

It seems that a more detailed guide is needed to get you access, however at the present moment we lack a wiki with pictures and translations. (We need help on this cause I suck at making wikis)

1: Get Chrome
2: Get Japanese Bandainamcoid
3: Sign up for Gundam Online
4: ????
5: Profit

It seems where everyone is getting stuck is step 4. That is a tricky spot as it requires a lot of system changing.

First get chrome, it helps as it will translate webpages with no issue.
Once you have Chrome, visit http://msgo.bandainamco-ol.jp/register/ and follow the guide using this guide. First get your ID with the orange button and then log in with the blue button. Your ID is your email address, it will have you check your email for access link and when that is done, download the installer.

The next step is a hard one as it will change your system to read Japanese.
Make sure you have the East Asian language pack vista/7 or the Japanese Pack for Windows 8 before setting your system locale as Japanese.

How to change system locale
Windows Vista/7 Ultimate/8

Open Region and Language by clicking the Start button Picture of the Start button, clicking Control Panel, clicking Clock, Language, and Region, and then clicking Region and Language.

Click the Administrative tab, and then, under Language for non-Unicode programs, click Change system locale. Administrator permission required If you're prompted for an administrator password or confirmation, type the password or provide confirmation.

Select the language, and then click OK.

To restart your computer, click Restart now.

After restarting your PC should read all text in the system as Japanese, this will now become tricky. 

Change your time zone to Tokyo UTC+9:00, this is important as it will enter a update/reinstall loop because the game will read that it is out of date. When the time zone is set, go ahead and install and patch it by pressing the orange button, the gray button will check and reinstall if needed.

When the game is installed and patched, you need to stop here and acquire a VPN. The best one is WTFast, it will allow you free access for 30 days, accepts paypal. There are free ones for normal VPN access, but it is not recommended for gaming.

Configure the VPN
Setting up the VPN is simple as long as you use WTFast, you have 1 for exe and 1 for launcher, you can also have it auto launch when you start up. Gundam online is not in the list of games yet, please do this as a custom game.

Once this is all done, you can now play the game, remember ID is your email!

Hope this all works for you, if not contact me at fatestaylancer on aim or on /m/