Rimuru has officially become a Demon Lord after defeating Clayman. Following Walpurgis, the Demon Lords' banquet, Rimuru's domain is expanded to include the entire Great Forest of Jura. Anticipating a flood of representatives from all races showing up to pay their respects, Rimuru decides to throw a festival to commemorate the opening of Tempest, using it as an opportunity to gain new citizens and present Demon Lord Rimuru to the world. Meanwhile, in the Holy Empire of Lubelius, home base of the monster-hating cult of Luminism, Holy Knight Captain Hinata receives a message from Rimuru. But the message is actually a fabricated declaration of war sent by some unknown party. Upon learning that Hinata is heading for Tempest, Rimuru makes a decision... Thus begins a new challenge for Rimuru, striving to distinguish friend from foe in his pursuit of the ideal nation where humans and monsters can prosper together.
Rimuru has returned to Jura after having attended Walpurgis. Diablo informs Rimuru of his mission to deal with the Kingdom of Falmuth. Having presented the kingdom with three options at a resolution, the clock on the week for their answer ticks down.
Yuuki is saddened by the death of Clayman, and Luminus is saddened by the death of Roy. Steeped in sadness, and having lost their friends, they seek their next move against Rimuru, who has grown in power and become a true Demon Lord.
Expecting visitors from all races to come calling after learning that Rimuru now controls the entire Great Forest of Jura, Rimuru decides to hold a festival to introduce himself and Tempest to the world, with the goal of attracting new citizens.
Responding to Rimuru's concerns about monsters in the forest harming humans, Vesta and Kaijin reveal a new invention they hope will keep the road to Tempest safe. Also, Rimuru assigns a new task to Geld.
A war council led by Hinata is held in the Holy Empire of Lubelius. Moments after Hinata declares her intent to meet Rimuru and talk to him, she receives a hostile message from Rimuru.
The spread of false information causes the Temple Knights to assemble, endangering Diablo's plan to conquer Falmuth. Meanwhile, Rimuru learns that Hinata is on her way to Tempest.
As Hinata makes her way to Tempest, the ramen and well-built roads she sees along the way prove to her that Rimuru genuinely wants monsters and humans to coexist. But against her wishes, one of her men is also on his way to Tempest...
The Crusaders have reached Tempest, and the battle is on. Hinata lays everything she learned from her mentor, Shizu, on the line in a life-or-death showdown against Rimuru.
Diablo descends before the enemy, King Edward of Falmuth. Also present are Saare and Glenda, two of the three Battlesages who are regarded as the most brilliant among the Master Rooks.
Just after the end of Hinata and Rimuru's duel, Hinata's sword moves on its own and targets Rimuru. Hinata jumps in its way to protect him and is gravely injured. Then the masterminds behind the whole conflict show up...
The Seven Days Clergy have been purged, and the battle is over. Rimuru and Hinata hold a meeting to discuss future relations between their two nations, and the masterminds behind the whole conflict, the Eastern merchants, are revealed.
Everyone in Tempest is busy preparing for the festival to celebrate the country's opening. Rimuru visits Mjöllmile to share ideas on forms of entertainment that will keep people coming back for more.
Demon Lord Ramiris tries to argue her way into moving to Tempest, where there's great food, hot springs, and ample entertainment. Rimuru happens to walk into the argument and comes up with a way to make use of Ramiris's skills.
Rimuru is building a dungeon in preparation for the upcoming festival. It will feature treasure chests containing weapons made by Kurobe, and Veldora will inhabit the deepest floor as the final boss. Then Milim suddenly shows up with a suggestion...
Numerous representatives from across the Great Forest of Jura have assembled in Tempest to congratulate Rimuru on his appointment to Demon Lord. Shuna requests holding a three-day audience to meet with them.
On the last day of the audience, Rimuru meets Momiji, the representative of the Tengu clan. Their meeting comes after Rimuru had sent Benimaru to the Tengu village to request their permission to build a tunnel through the Kusha Mountains.
After learning about an elf slave trade, Rimuru had Soei investigate, but it turns out the slave traders have already been shut down by Masayuki, the Lightspeed Hero. Word is now spreading that the Hero is headed to Tempest to slay a Demon Lord...
After meeting with the kings of various nations, Rimuru heads to Engrassia to invite his former students to the festival. The kids are thrilled to go back with him to Tempest, but then the hero Masayuki arrives as well...
The night before the Opening Festival, Rimuru throws a lavish banquet for all the nobles and royalty visiting Tempest. When the party is in full swing, Empress Elmesia of the Sorcerous Dynasty of Thalion arrives, throwing everyone into chaos.
It's day one of the festival, and Rimuru finally gets to see all of his friends' performances and presentations. As he's enojying the festivities, he's summoned by Luminus...
A martial arts tournament is being held! The winner will be given the right to challenge Rimuru. The hero, Masayuki, will be participating in the tournament. Rimuru wants to uncover the hero's true strength, so they get Geld and Gobta to participate.
Gazel and Elmesia pledge to assist Rimuru with Tempest's lack of funding. Elmesia then proposes an alliance, but she's concerned about the danger Diablo poses.
Rimuru's dungeon is finally revealed, and his new ally Masayuki is among its first challengers. Later, after the festival is over, Rimuru's biggest job still awaits.
Rimuru pays the merchants with the gold coins he's procured. The merchants try to garner futher favor, but Rimuru ceases trading with them. Rimuru then gathers his allies and calls for action again the eastern merchants who are operating in secret.
