After Mundus reawakening event. Yn and Nero make their way toward "Demon World" itself in order to destroy the Demon Army. Their journey continue. New friend and enemy are waiting to be found. Meanwhile, Rias and V was planning to bring Yn and Nero back to the human world. However, It's not an easy task. Since the key to unlocked the door to the Demon World was in 'someone' hand who might not have any interest on visiting the Demon World... Again.