They didn't. The manga looked at the game and is doing great so far (as opposed to the anime, it has everything that looked cool, and the additions are well done, again unlike the anime), the anime looked at neither the manga (which didn't exist at the time) nor the game.
It's as if they didn't even look at the manga and started to make up their own little stories.Maybe they looked at the game?
If I struggled to the end of my determination, to the end of my way of life with my followers, if the result is ruin, then this ruin is inevitable. Grieve. Shed tears. But you cannot regret.