My Reincarnation as a Slime. Book 6

Children from another world, transported here by an incomplete summoning ritual, lived in fear of the destruction of their physical bodies due to the instability of magic within them. But Rimuru found a way to save them. For this, he, along with the children, goes to the 'Spirit's Nest'...
Meanwhile, the western states, dissatisfied with the rapidly growing power of the country of monsters they despise, took advantage of Rimuru's absence and attacked his capital, Tempest.