Voir That Time I Got Reincarnated as a Slime, Season 3, Pt. 1 - Uncut - Episode 1

After defeating Clayman at Walpurgis, Rimuru officially became a Demon Lord and a member of Octagram. Meanwhile Diablo awaits Rimuru's return in Tempest, and is anxious to learn about his master's activities as soon as possible. A look back at Walpurgis.