Simulacrum

The universe accidentally created by the Humi. Once but a simulation, the Simulacrum "realized itself" and actualized in reality. It now unnaturally encapsulates the Starlyng Universe like a membrane.  Humi, Firstborns, and the Unknown are the only groups aware of the Simulacrum's existence. The "entrance" to its "heart" is through Davy Jones's Locker. 

Barring certain exceptions, all modern EUB originate from the Simulacrum. Prior to the birth of the Simulacrum, other extrauniversal beings were able to slip into the Starlyng Universe, but this is no longer the case. The Simulacrum's "imaginary-real" composition is nigh impassable to most entities (even Simulacrum EUB can only enter the Starlyng Universe; they cannot go anywhere else. Firstborns find traversal painful and thus avoid it. Unknown are the true outliers), making it both an unintentional shield and a double-edged sword. 

Simulacrum EUB invade with a frequency unlike all other, former EUB, hence the expansive prevention efforts of the Order today. (The Ordo Originis does not make a distinction between Simulacrum and non-Simulacrum EUB. They are [intentionally] uninformed of the difference, and, save for the Unknown, all present-day EUB hail from Simulacrum.)