My Reincarnation as a Slime. Book 7

While Rimuru was absent, the country of Tempest was covered by a double magical barrier. It isolated the country due to its antimagic effect and caused weakness in the monsters. Because of this, Rimuru couldn't immediately return to Tempest, and the city suffered significant damage.
Rimuru feels the need to take responsibility for the situation caused by his recklessness, so he sets out alone to battle the enemy — the army of the Falmu Kingdom.