Jojo's Bizarre Adventure: Diamond Is Unbreakable is being released on 13 DVD or Blu-ray volumes. Each disc comes with one entry coupon, and you need to send all 13 coupons to receive the bonus OVA. The last 13th DVD/Blu-ray volume is scheduled to be released on June 28, 2017 and a new visual is anticipating the unaired episode.
That bonus will be based on the 46-page 5th episode of Hirohiko Araki's Kishibe Rohan wa Ugokanai/Thus Spoke Kishibe Rohan manga. Mai Nakahara and Kaori Mizuhashu joining the cast.