The facility was destroyed during the Blue Night, leading to the formation of the Exorcist Cram School. Mephisto Pheles stored Section 13 in a separate dimension, preserving it for investigation ...

Another important element in Blue Exorcist: The Blue Night Saga episode 2 was Rin Okumura discovering the truth of how Mephisto was creating several demon king clones to get Lucifer a new body.