According to the official website, an extra episode of Kurokami
will be included in the final volume of Blu-ray/DVD. A preview of the episode titled "Side Story: Tora to Tsubasa (Tiger and Wing)" will be held on August 9th at Young GanGan Fes.
Synopsis of the episode:
Half a year after the battle in Okinawa, Excel was looking for a new Motosumitama to revenge on Reishin. Excel met Mikami and decided to contract with her. Before making the contract, Excel looked back the encounter with Steiner.
Source: Kurokami official website