No release date, platform or region has been announced yet. Source: Official announcement
The official Mushoku Tensei website announced new character information for Kishirika Kishirisu, who appears in Episode 9 of the third season of 'Mushoku Tensei: Jobless Reincarnation'. This episode is titled 'Dōkoku'.
Information obtained from the official Mushoku Tensei website.
Official source: mushokutensei.jp