22/7: 8+3=?

Extra thirteenth episode included in the sixth Blu-ray & DVD volume of 22/7.
22/7 was revived for the fans on December 24th, which was their day of formation.The next day, when eight people came to the office, the Wall was completely revived, and the mystery only deepened. To dispel the disturbing feelings, Sakura proposes to have a Christmas party to celebrate the reunion.
(Source: Funimation)