That Time I Got Reincarnated as a Slime, Vol. 4 (light novel) (That Time I Got Reincarnated as a Slime (light novel))
NO REST FOR A NATION-BUILDING SLIME!
Now that Rimuru's monster-centric town has blossomed into a bona fide independent nation, it's time for his next step: build and maintain diplomatic relations with nearby countries! With a group of his trusty monster pals, Rimuru travels to the Beast Kingdom of Eurazania and the Dwarven Kingdom to meet with their respective heads of state and represent his domain as best as a slime possibly can. As if there wasn't already enough on Rimuru's mind, the otherworlder Shizu has been visiting him in his dreams, begging him to save her former students. Looks like that'll be another stop on this pliable pioneer's itinerary...