That Time I Got Reincarnated as a Slime manga omnibus volume 3 contains volumes 7-9 and features story by Fuse with illustrations by Taiki Kawakami.

The danger of the Orc Lord has passed, but Tempest has a new problem, Demon Lord Milim. She's decided to take up residence in the monster nation, and her presence attracts the servants of a rival demon lord. As the leader of the Jura Forest Alliance, it falls on Rimuru to resolve this threat, but that's far easier said than done. How could anyone, even the mightiest slime, hope to manage an all-powerful, child-like Demon Lord while managing an entire nation of monsters?