"The Demons' Breeding Season"

When the World Union knew that the demons went to the Four Seasons island to breed freely so as not to be caught back in the abyss so easily, they immediately informed the people from Elton Academy. 

"Most of the demons are actively trying to be teleported to that island through the dimensional hole, and we think they vaguely know which dimensional hole will lead to the four seasons Island." 

Because of this, the World Union sent reinforcement to Elton Academy, and the guild alliance, plus free ability users, were also relocated to Elton Academy. 

If they wanted to catch all the demons and stuff them back into the abyss, the four seasons island might be a good way to gather almost all the demons and teleport them all back to the abyss. 

The fairy of space could definitely do this, but they also had to enter the island to make sure all demons were gathered in one place, and none were hiding somewhere to breed.