The Aether Gates that opened within the Sea of Sands were quite similar to the one that had opened on the Central Island, although not quite the same.
The Rift that had opened on the Central Island led to a sub-realm located on the edges of the Aether Realm. Because of its location and position, this was also why Aether leaked through the portal and into the island, infecting the humans that had been there.
While thid was not the cause of their mutation, it was the reason why they couldn't use mana as well as regular humans. Instead, their bodies were better suited for Ki and Aether, although controlling the latter is a fool's errand.
The similarity between the two is specifically the property of connecting separate realms together.
These Rifts are not simply rips in space-time. Rather, they are something more profound.
They occur when an incredibly great influence is exerted onto a space, such that the space cannot bear the strain anymore.
