If you want to break through to the eighth tier, not just any place will do. First, you must find a world that has reached above the eighth tier; this is a hard rule. This rule is something that no one can change.
Among the worlds under Du You's command, only the Tangled Undead World has reached the eighth tier.
However, this world has already locked its upper limit and does not allow advancement to the eighth tier. This is to prevent a demon invasion from the outside world. It's impossible for Du You to advance in this world.
Using other worlds controlled by Earth is also possible, but very few people choose this option.
After all, the higher the level of the advancing world, the faster the advancement speed. The effect depends on oneself.
Du You chose to advance on Earth; without a doubt, this is the safest place.
