Since Eternum's Android change, there have been quite a few people that struggle with installing the game. I'm creating this post to have all-in-one instructions & FAQ so I don't have to explain the same things over and over to different people.

First of all, this is how everything looks on my device! Your device might look different but the gist should be the same.

1.  Dowloading the game

Click the download button on the game page.

Eternum is a great game you should support financially, but if you're just trying it or or are supporting the dev on other platforms you can just skip straight to the downloads.

Scroll down

Download the Android version

Confirm that you really want to download this file

After the download process is complete, find the file in your download folder. I'll now show you how to navigate to the downloads folder and I then expect you to know how to do it for rest of the tutorial!

Open your file explorer/manager app

Make sure you start off in the root directory of your device! This is how it should approximately look like; open the download folder.

There's the file you downloaded. Check whether the file size is plausible, it's around 3.5 GB for 0.7. If you have way less, your download is corrupted! See the troubleshooting section below. I doesn't have to exactly match since there are different ways to calculate the size of a file. 3.3 GB would prbly be fine too for example.

Troubleshooting

If your download fails midway or won't start at all, try again with a different browser. If your file is smaller than it should be, your download is corrupted/incomplete. Delete the file and also try again with a different browser.

2. Installing ZArchiver

We'll use ZArchiver to secure our old save files (if we have any) and to extract the game files from the zip file we just downloaded.

Open the Play Store:

Search for the app "ZArchiver".

Install ZArchiver.

Open the app.

You need to grant permission for it to access your file system.

Flip the switch, then return.

Close the mini tutorial.

3. Secure your old save files

If you already played Eternum before, you'll need to secure your save files if you don't want to risk losing them!

In ZArchiver, go to the Android directory

Then go into "data"

Now, Android/data is a very special directory in Android and that's why ZArchiver needs special permissions to access it. Click ok...

Nothing to see here, just click the button at the bottom...

Allow...

Now find the folder for Eternum in there

saves...

And there they are! We're going to copy all of them. You don't really need every single one but please pick at least a few, like the 10 most recent ones + the one named persistent a the very bottom. If you just copy a single save you 1.: lose all the lewds you unlocked in the gallery because you didn't carry over the persistent file and 2.: if the one save ends up not loading properly, you've lost everything and all of this was pointless.

Also keep in mind that if you carry over let's say a save named 36-2-LT1.save, that save is always going to be on page 36 of the loading screen!! You can rename it to a lower number than 36 to place it on another page though. Just make sure you don't have duplicate names and the second number shouldn't be higher than 4 (or 6, if you have a big screen).

Multi-select...

I'm not manually selecting 175 files...

Select all...

Confirm selection...

Now that they're all selected we can copy them...

Copy...

Ok, we're in copy mode now. You can now navigate to a folder of your choosing to secure your files there! Click the topmost option to navigate back out of a directory you're in. To get back to the root folder, you need to do this 5 times.

I've navigated into this empty folder here and I'm now new creating a new folder to store my saves in.

New folder, give it a name...

Now we're in the new folder and can put our files in here!

And we're done. We'll use these files later. You can now uninstall the old version of Eternum without having to worry about losing your saves!

4. Unpacking the zip file

Your device might be able to unpack/extract zip files by default but I had at least one user whose zip extractor was very unreliable and it spat out incomplete files that didn't work. Use other means of extraction if you wish but I think it's best if you just do it like I'll show you now.

Open ZArchiver and navigate to our download folder

Here's your downloaded file again. Notice how the file size is different from before? As I said, there are different ways to calculate file size. Click on the file.

Now, select this option to begin extracting the contents of the zip file:

This should take a moment. Feel free to hide the screen and do something else in the meantime.

After it's done a new folder pops up in the download folder:

But ZArchiver has done its job now. Using your file manager, navigate to the downloads folder and open the folder we created just now.

5. Installing the game

In our new folder, you will find 3 files. Click to install the .apk file on your device

Installing apk files can be dangerous! Always make sure you can trust the source you downloaded it from. Here, we need to give our file manager permission to install apk files.

Flip the switch in the settings. Again, always make sure you can trust the source you get your apk files from!

Now the installation process can begin; click install.

This should take just a moment. You can open the app right after.

On first startup, you need to grant the app permission to access your file system.

The game will now create the directories you need later. Click.

And now click anywhere to close the game again.

Let's follow these instructions! Find the folder we created earlier to start moving the archive.rpa file.

Now click move...

Select the archive.rpa file and then click move again...

Okay, now we need to locate the game folder! Just follow the pictures: Internal storage...

Documents...

Ixalon... (This is a folder the game just created!)

com.caribdis.eternum...

And finally game...

Now you drop off the file here and that's it!

This is how it's supposed to look like:

And the game should now start properly once you open it again:

If everything works you don't need the zip file and the folder we created in the download folder anymore. You can delete them.

Known issue

Some people have reported that despite installing everything properly, their audio doesn't work (save for the intro when opening up the game) and all animations just show black screens instead. Though the game still diplays pictures and dialogue and doesn't crash on startup. If you're experiencing this too, it's probably not your fault, but a bug. If you're experiencing the same thing, please write a comment below! We might contact you back in an effort to figure out what the issue is. In the meantime, all you can do is either be patient or use another device to play :(

6. Carrying your saves over

So you have secured saves from the previous game versions and want to keep using them? To do that, we will ERASE ALL PRESENT SAVES first. If you want to keep those, see section 3 above on how to secure them before they are lost forever.

Go to its storage settings...

And now clear all app data to basically reset the app to its original form

This is how it looks like afterwards:

It's important that you don't open the Eternum app by accident right now! If you do, start over with this section. Otherwise, navigate to the directory where you copied the archive.rpa file into. Don't go into the game directory but the directory right before that! 

Delete all files and folders in this folder EXCEPT the game folder. We wouldn't want to undo our progress, right?

Now find the saves you want to carry over and copy all of them...

...copy all of them...

...into the folder where we just deleted the other files!

And now opening the game again will again prompt you for file access permissions, which you need to grant, but your save files should be there now!

If your game warns you that the files might be from a different source and you should be careful, simply continue as long as you're sure these are actually your files. If you get an error message like this:

Quit the game and try another save! Most saves should still work. Saves you made after major scene transitions have a higher probability of loading successfully!