That Time I Got Reincarnated as a Slime Season 4

The Founders Festival has ended in great success, and the Jura Tempest Federation takes a new step toward realizing the Human-Monster Prosperity Zone. While Rimuru Tempest is inspecting the town, he encounters adventurers arguing with Benimaru and the security team over conquering the Underground Labyrinth. After receiving complaints about the dungeon's difficulty, Rimuru Tempest gathers Veldora Tempest and others for an operational meeting. As Rimuru Tempest frets over the low level of the challengers, Masayuki proposes a game-like solution.

Thanks to Masayuki's idea of opening rest areas and the publicity from the high prize money, the dungeon overhaul is a huge success! While Rimuru is relieved that management is on track, a party named "Team Green Rebellion," consisting of 100 members, arrives to conquer the dungeon. Furthermore, Hinata's training in the dungeon has caused the Floor Guardians from the 60th floor onwards to become non-functional. In response to this emergency, Rimuru sets out to strengthen the dungeon.

Rimuru and his friends have obtained avatars for the underground dungeon. However, with low-level avatars and uncoordinated combat styles, they are no match for Team Green Fury. Consequently, Rimuru begins special training with his companions.

Even after repelling Team Gekiran, Rimuru and the others continued their special training in the underground labyrinth. Meanwhile, at the Council of the West in the Kingdom of Ingrassia, a certain discussion regarding the Jura Tempest Federation was being held.

Rimuru and his companions arrive in the Kingdom of Ingrassia following a summons from the Council of the West. When the Jura Tempest Federation requests to join the Council, the councilors present conditions driven by greed.

Rimuru is infuriated by the unreasonable demands from the Council. Furthermore, Prince Elrick of the Kingdom of Ingrassia appears, seeking to subjugate Demon Lord Rimuru, throwing the council into a volatile situation.

Having successfully prevented the assassination of Elrick amidst the chaos, the council concludes safely with the Jura Tempest Federation joining. Upon returning to the Jura Tempest Federation, Rimuru and the others begin interrogating Glenda, the perpetrator of the assassination attempt.

Yuuki is controlled by Mariabell. Upon receiving information from Glenda, Rimuru decides to avoid interacting with the Free Association. However, the scheduled day for the ruins investigation with the Free Association was drawing near.

Rimuru and his companions arrive at the ancient ruins of Amrita. Although the group's investigation is proceeding smoothly, the ruins' defense mechanism suddenly activates and attacks the survey team. Furthermore, Mariabell makes an appearance...

Mariabell, who possesses the unique skill "Greed," and Rimuru, who has awakened as a Demon Lord. The difference in power between the two was obvious. Rimuru attempts to defeat Mariabell, but Yuuki stands in his way.

Demon Lord Milim confronts the Chaos Dragon that she herself once sealed away. For the sake of Milim, who cannot bring herself to defeat her friend, Rimuru aims to protect the soul remaining inside the Chaos Dragon.

With Mariabell's control broken, the Jura Tempest Federation has become the largest faction in the Council of the West. While facing a mountain of problems, Rimuru takes a breather by inspecting various locations, only to receive an urgent message from Ramiris.

Rimuru begins working in earnest on creating the physical vessels requested by Diablo. However, due to the sheer quantity required, the research lab is facing a severe shortage of hands. Just then, Rimuru is saddled with looking after Demon Lord Dino by Demon Lord Guy. Hiring Dino to work in the lab, the group continues creating the vessels. Then, Veldora chimes in, demanding that he wants an assistant of his own as well...

Diablo, having left Rimuru's side, has arrived in the underworld. In order to delegate his miscellaneous chores in the Jura Tempest Federation, he visits three demons who are old acquaintances of his.

With new allies joining their ranks, the Jura Tempest Federation begins to take its first steps as a nation ruled by law. Meanwhile, as Rimuru and the others move forward, Laplace and his associates, disguised as "Eastern merchants," make contact with Demon Lord Leon in the Golden Land of El Dorado.