Story
The third season of Tensei Shitara Slime Datta Ken. Rimuru has officially become a Demon Lord after defeating Clayman. Following Walpurgis, the Demon Lords' banquet, Rimuru's domain is expanded to include the entire Great Forest of Jura. Anticipating a flood of representatives from all races showing up to pay their respects, Rimuru decides to throw a festival to commemorate the opening of Tempest, using it as an opportunity to gain new citizens and present Demon Lord Rimuru to the world.
Synopsis via AniList (English).