"Revealing Transmigrators" 

"A spatial attribute alone is not enough, because only the fairy of space can control space outside of our world." 

The abyss was like a completely brand new small world, so to block the passage between the two worlds, they at least needed the power of the fairy of space. 

But this required a lot of energy, and to maintain the seal for so long, just one fairy of space could not do it. 

Not to mention that this fairy still had responsibilities related to space matters inside the world itself, such as suppressing the dimensional holes' growth, and so on. 

"So, we need something that has an otherworldly attribute to block the passage between the two worlds. We discovered that the energy from souls can barely block the passage between the two worlds." 

But what kind of soul?