That Time I Got Reincarnated as a Slime season 2 episode 8
Episode title: Hope
Rimuru learns about Clayman and the schemes of the Kingdom of Falmuth, but no matter how hard he wishes for it, his fallen comrades and their peaceful lifestyle will never return. He's just about to give up when Eren tells him of a fairy tale that might offer a glimmer of hope. The probability of success is about 3%... but if Rimuru can manage to become a Demon Lord by taking in the souls of 10,000 humans as nourishment, he just might have a chance at bringing his comrades back to life. As Falmuth's army of 20,000 men marches toward Tempest, Rimuru takes hold of that hope and decides to become a Demon Lord.
