Bundled with the 12th and 13th limited-edition volumes of the light novel. The "first episode" was originally supposed to be bundled with the 11th volume but had production delays, it will now ship with the 13th volume in December 2019. Another OVA was announced to be bundled with the 12th volume release in July 2019.
The episode bundled with the 13th volume will be about the Sumo competition that held at Tempest for the first time, suggested by Rimuru.
(Source: MAL News & ANN)
