Physics of the character controls...
While Hack Sign doesn't delve deeply into how characters are controlled, they do take certain moments to point out that, in fact, what we are watching is being controlled(theoretically), by the users in the Real World via a controller and headgear for visualization.
At one point, Mimiru goes 'afk' and her character freezes until she returns, probably just illustrating that there is limits to the World's character activity.
But how could the makers of the World possibly anticipate every single emotion/activity/movement these avatars can and do make?
There's too much animesque free movement for this to be a video game world. Too many variables!!
How is it supposed to work? They are using analog-stick controllers, like the Game Cube's. To turn around, walk, smile at eachother, nod their heads, jump, move eloquently. For hours...