According to official Twitter account, an original video anime of comedy romance anime series Boku wa Tomodachi ga Sukunai was announced.

The said un-aired 13th episode will be released on September 26 and it is titled “Boku wa Tomodachi ga Sukunai: Add-on Disc.”

Synopsis
Hasegawa Kodaka is a recent transfer student to St. Chronica’s Academy, a Catholic high school. As with every other school he has ever attended, he finds it difficult to make friends there because of his naturally-blond hair and fierce-looking eyes, which make him look like a dangerous “yankee” to his prejudiced schoolmates. One day, Kodaka accidentally comes across the equally solitary and very abrasive Yozora Mikazuki while she converses with her imaginary friend Tomo. Realizing that neither of them have any social lives, they decide that the best way to improve their situation is to form a club: the Neighbor’s Club precisely intended to make friends and learn social skills. 

[Source]