That Time I Got Reincarnated as a Slime, Vol. 18 (Light Novel): Volume 18

ANGELS AND DEMONS AND MONSTERSThe seraphim force led by Michael proceeds with its plans for invasion, and the Octagram's eight demon lords assemble once more for a Walpurgis Council to determine their response. They need to act fast, for Michael's Ultimate Dominion skill has brought even Velzard--a True Dragon and Veldora's eldest sister--under his control. How will they solve this conundrum? Rimuru isn't sure yet, but as he readies Tempest for war, he'll soon discover a lot of his problems are much closer to home than he thought...