Mikami Satoru wakes up after dying, having found himself to have been reincarnated as a slime. After exploring the cave he finds himself in, he meets his first friend in this new world, a True Dragon named Veldora. Upon taking the name Rimuru, he sets out on his quest to defeat the Devil King, and in doing so, use the wish he gained from doing so to free Veldora from his Unlimited Imprisonment. The path there, however, is a bit more chaotic than they anticipated.