Ao no Exorcist

Synopsis

Rin, Yukio, Shura and Arthur join forces to bring down the Gehenna Gate, but with no success. Meanwhile, demons keep coming through it and giving a hard time to the other Exorcists until the Exwires come up with a plan to open a gate to the Vatican, where it is already daytime, and reflect the sunlight there to the Academy, where it is nighttime, to weaken the monsters protecting the Gehenna Gate. Rin and Yukio manage to seize this opportunity and, when both unlock their demonic powers together, they fly through the Gehenna Gate and destroy it. One month later, things are back to normal at True Cross Academy and the Okumura twins pay a visit to their mother's grave before returning to their duties as Exorcists.

(Source: Wikipedia)