It's using a plugin system for various sources, basically it's just a fancier front end for the source websites. it is not hosting its own (illegal) content.
yeah, they are trying to sue tachi since most of plugins were tachi's own plugins. idk what the copyrights holders are going to do now since the unofficial plugins are out.
You need to set up quite a few things first. It's like suing an app store cause you can install a browser and pin a piracy website to your home menu, giving you one click access to illegal sources.
The app came with a fairly large extension list pre-populated so it's a little different to a browser. Although a browser with all the piracy links already bookmarked would be rad.
Either way, you can still point the app towards any other repository so it doesn't really hurt for them to remove the default extensions repository to avoid potential legal problems.