A two-episode special. They are designated as Episodes 13 and 14, and the first episode is a direct sequel to the previous series while the second episode is about the trans-sex of Natsuru.

Ryouhei Arisu is a high school student with no ambitions and just wants to escape from what he feels is a meaningless reality. One night when he is with his two friends Daikichi Karube and Chouta Segawa, they see an abnormally large firework shoot into the sky, an event which signals a permanent change in their lives. Blinded by the incredibly bright explosion, the three find themselves transported to what is known as the Borderland. The only inhabitants of this world are participants of a deadly game where specific tasks must be accomplished if they wish to survive. As the three begin playing to determine how they can get back home, Ryouhei finds himself feeling alive for the very first time in his life. [Written by MAL Rewrite]

OVA bundled with Niθ Art Works Vol. 2, featuring a new character named Kagekatsu Uesugi.

In a post-apocalyptic world overrun with mutated beasts called Limbeekoon or Filth Monsters, humanity is forced to live in large mobile cities called Regios and learn to use special weapons called Dite, by harnessing the power of Kei to defend themselves. In the Academy City of Zuellni, Layfon Alseif is hoping to start a new life and forget his past. However, his past has caught the attention of Karian Loss, the manipulative Student Council President and Nina Antalk, a Military Arts student and Captain of the 17th Military Arts Platoon, who instantly recognizes his abilities and decides he’s the perfect candidate to join her group. However, with a secret past that won’t leave him alone and unknown powers beyond normal, Layfon just might not take it.