Phobio can't restrain his anger toward Milim. He finds himself faced with Footman and Tear, two masked members of the Moderate Harlequin Alliance, who suggest that he become a Demon Lord to take revenge on Milim. They tell him that he can accomplish this using the power of Charybdis. Meanwhile, the Jura Tempest Federation sends Youm out on a journey to make the world believe he was the champion who defeated the Orc Lord.

Its seal removed, the calamity-class monster Charybdis and its Medalodon minions advance on the capital city of Rimuru. The Jura Tempest Federation combines all its forces under Rimuru to intercept the attack. King Gazel even sends 100 of his Pegasus Knights to aid in the battle. But Charybdis's extra skills Magic Jamming and Ultraspeed Regeneration make it a formidable foe. So Rimuru unleashes his new skill, Gluttony...

A new force has suddenly risen to power in the Great Forest of Jura, and its leader, Clayman, proposes that the Demon Lords hold Walpurgis with the goal of sanctioning the slime who deceived him. Rimuru also begins to prepare for a battle with Clayman, but observing the enemy army's movements reveals that Clayman's target is not Tempest, but Eurazania. Clayman's army will arrive in Eurazania within two days. Can Rimuru's forces get there in time?

To put a stop to Clayman's plans, Rimuru uses transport magic on a large scale to both move Tempest's army to Eurazania and evacuate the people of Eurazania to Tempest. Rimuru also decides to crash Walpurgis, the Demon Lords' banquet, in order to settle the score with Clayman personally. Since this will be a return match for Shion, he decides to take her and Ranga along. New military forces are organized in Tempest in preparation for the battle against Clayman's army. At last, the eve of battle is upon them...

With all the preparations complete, Rimuru heads out to attend Walpurgis with Shion and Ranga, while Ramiris takes Beretta and Treyni. In the meantime, Shuna, Hakuro, and Soei find both their vision and their magic detection abilities hindered by a thick fog as they draw closer to Clayman's castle. From within the fog appears the Index Finger of Clayman's Five Fingers, Adalman, also known as the White King. Hakuro and Soei hold the enemies around them at bay while Shuna faces Adalman one-on-one.