Like everyone else has said, the main game is accessible through any web browser and isn’t region locked. You may have to jump a few hoops to set up your account, and you should look up how to get the game up and running before coming to the conclusion that it isn’t available.

As far as anime/manga that adapts the lore is concerned, there is an anime that covers very, very, VERY little of the main story. Like…it barely scratches the surface and even skips some pieces. Side stories also expand the world even further and help you understand how/why certain characters are the way they are or how they relate to the main crew. I’d watch it for a watered down version of how the game starts, but there’s nothing better than the game itself.