Tensei shitara Slime Datta Ken: Coleus no Yume
English title: That Time I Got Reincarnated as a Slime: Visions of Coleus
Japanese title: 転生したらスライムだった件 コリウスの夢
Type: ONA
Episodes: 3
Source: Manga
Genres: Action, Adventure, Comedy, Fantasy
Studios: 8bit
Duration: 24 min per ep
Rating: PG-13 - Teens 13 or older

The story takes place between the first and second season, where Rimuru confronts the swirling conspiracies in the Coleus kingdom.

(Source: MAL News)