Perfect Realm Domination. When the caster masters the skill, they create a world that's completely their own. Unlike the regular Realm Domination, the Perfect Realm Domination cannot be overpowered by another cast of the skill.
It is an entire realm filled with real people, real places, and real set of rules. The caster has the absolute control over what happens in the realm, how the simple natural aspects of the world we know works.
The only way to deactivate it is when the caster dies or deactivate it themselves, and in this case, they have to find Sayu and defeat her. After the woman's cast of the skill, everything became a race against time.
Since Sayu had complete control over her realm, she can alter anything in the world. This takes massive amount of magic that it is forbidden to be used. Casting the spell alone will deplete the magic of the caster, killing them.