Tensei shitara Slime Datta Ken OVA
転生したらスライムだった件 OVA, TenSura OVA, That Time I Got Reincarnated as a Slime OVA
Bundled with the 12th and 13th volumes of the manga. The first OVA will be about the Sumo competition that is held at Tempest for the first time, suggested by Rimuru.