Help Required in Ripping a Japanese android game [The Prison Boys]

[Stryquill]

Base .apk files usually don't contain the entire game, which is why you end up having to download data in the game itself.

Easiest way around would be using a rooted Android (or Android emulators) and browse for its data within the SD card. Where the folder is depends on the game but it's pretty easy to spot since they're usually named com.(developing company name).(game name). After that it's just pulling out all the files from there.
Most Android games tend to use Unity, so if you find files with no extensions you might want to check this thread out: https://www.vg-resource.com/thread-31141.html

There is no download data in the game itself. I think you meant its .obb files. Well, it doesn't have it. And yes I actually did search through the SD card through an Emulator... Sadly didn't find anything. And no there's nothing related to Unity or so I seem to remember