Rimuru sends a delegation led by Benimaru to the Animal Kingdom of Eurazania, ruled by the Demon Lord Carrion, also known as the Beastmaster, to establish diplomatic relations after becoming indebted to him in the battle against Charybdis. A delegation from Eurazania is set to arrive in Tempest around the same time, but the Animal Kingdom is a very warlike nation, and Shion is enraged when one of the delegates, Suphia of the Three Beastketeers, makes a belittling remark toward Rimuru. The goal was a friendly relationship, but it takes no time at all for a fight to break out...

Despite the initial conflict, Eurazania and Tempest have deemed each other to be worthy of establishing friendly relations, and diplomacy between them officially begins. Tempest agrees to share its industrial techniques in return for Eurazania's agricultural techniques, and Rimuru decides to use the apple brandy produced as a result of this exchange to seek friendly relations with the Armed Nation of Dwargon next. He's accompanied by Shuna and Shion along with the former residents of Dwargon, Kaijin and the three Dwarf brothers, who are welcomed back to their home nation as state guests.

Following Clayman's orders, Myulan ignores the words of Youm and Grucius, both of whom have fallen in love with her, and activates the Anti-Magic Area spell. At the same time, Reyheim also activates Prison Field. The double barrier prevents Shion and the other fighters of Tempest from fighting as well as usual, and they end up at a disadvantage in their fights with three Otherworlders. Benimaru tries to contact Rimuru, who still hasn't returned, but he can't even get in touch with him due to the barriers.

Shion and the rest of the fallen are revived, Diablo has joined the team... It seems as if all is going smoothly, but Rimuru then receives a report that Milim has declared war and Eurazania has been destroyed, and there's still the matter of the Western Holy Church's hostility toward monsters, even with Falmuth out of the picture. But at the same time, Raphael informs him that the Appraisal of Unlimited Imprisonment has been completed. At last, two years after Rimuru's reincarnation into this world, he can finally fulfill the first promise he made here: to free Veldora.

A feast is thrown to celebrate the revival of Tempest's fallen and the return of Veldora. After enjoying a brief, peaceful respite, Rimuru tells everyone his future plans: he's going to get the word out to the whole world that he's a Demon Lord and declare war against Clayman. Then King Gazel of the Armed Nation of Dwargon, Fuze of the Kingdom of Blumund, and Eren's father, Archduke Elalude of the Sorcerous Dynasty of Thalion, all arrive in Tempest, and an important meeting to discuss the nation's future begins.

Rimuru announces his plan to back Youm as the new king of Falmuth. After hearing this, Gazel tests Youm to see if he has what it takes to be a ruler, and Youm answers with full sincerity. Erald also takes a liking to Rimuru after hearing him say he just wants to create a world where everyone can prosper and smile. Thus Rimuru and his allies look ahead to the battle against their new enemy, Clayman.

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...

Rimuru continues with preparations for Walpurgis, including making Treyni evolve into a Dryas Doll Dryad. Meanwhile, Benimaru and his forces have arrived in Eurazania via transport magic, and they promptly run Clayman's army into a trap set by Geld. The Three Beastketeers, determined to rescue Carrion, set out to subdue the enemy army's leader. Albis fights one-on-one with Yamza of the Five Fingers, while Phobio takes on Footman and Tear.

Gabiru narrowly wins his battle against Hermes. Watching their outcome is Middray of the Dragon Faithful, whose skill was enough to overwhelm even Suphia. Though he looks like a human, he is actually a Dragonewt like Gabiru. Meanwhile, Yamza uses his artifact Doppelganger to create a double of himself, but Albis still defeats him soundly. He tries to surrender, but Clayman takes control of him and forces him to transform into Charybdis.