That Time I Got Reincarnated as a Slime season 4

As Shuna searches for Rimuru, the latter observes Tempest and sees how monsters and humans have been getting along. He has also made plans to build a train station for the new train and a bar with female elves on the Dungeon’s 95th floor. However, Rimuru also learns that the Dungeon has been having issues. Meanwhile, Hinata teaches class in Tempest, with Class S being among them, but when she catches Rimuru in the classroom, she throws him out. After Shuna finds Rimuru, she gives him a new type of dish: pudding that resembles Rimuru himself, which he shares with Veldora, Ramiris, Gard, and Masayuki. While talking about how to improve the Dungeon, Masayuki gives Rimuru some helpful ideas such as save points, bathrooms, restaurants, and tutorials, while Gard creates advertisements to attract adventurers with the promise of reward money. After Shion makes tea for Rimuru, Diablo accepts no reward for his help in taking control of Falmuth, but he does wish to have his own subordinates. Rimuru also has Souei keep an eye on Muese to find out more about his background. In Engrassia, Yuuki is unable to progress with his plans now that Rimuru is onto him, so he decides to be neutral towards Rimuru despite concerns from the Alliance, but he also continues his plans in the West. Meanwhile, Mariabel and Granville begin their plans to destroy Tempest in favor of a former Chosen Hero.

Team Lightspeed try out the Dungeon again. After clearing the 30th floor, Masayuki's fame rises. Rimuru, Masayuki, Ramiris, Grad and Veldora are pleased to see how the Dungeon is functioning. They also learn that another group called Team Green Fury is clearing the Dungeon quickly. Ramiris and Veldora are paid for their hard work. Also, merchants from the Western Nations are visiting Tempest. Private research labs for Rimuru and Ramiris are built in the Dungeon. Shion and Shuna visit Rimuru during this time to let him know that Grad needs to talk to him. Grad reveals that Team Green Fury have also cleared the 30th floor. It turns out that the party has been increasing their members and using save points before a boss fight, which will be a problem for the Dungeon. Rimuru also learns that the bosses on the 60th and 70th floors have been experiencing issues and the Crusaders training in the Dungeon are having their own problems, leading Hinata to take on the Dungeon herself. She managed to clear the entire Dungeon, but couldn't beat Veldora. Rimuru isn't willing to reward her though. He, Shion, and Shuna visit Adalmann, who lost to the Crusaders since he can't use Holy Magic anymore. After helping him develop new magic attacks, they provide him with his throne room. They still have to resolve the problem with Ramiris's Elemental Colossus, which can't respawn. Milim returns with Ranga and Gobta, having finished their training. She is shocked to learn that the dragons that she caught for the Dungeon have been beaten. Ranga and Gobta are rewarded for their hard work. Upon learning of Team Green Fury's progress, Rimuru makes new devices that create avatar monsters based on their thoughts and transfer their consciousnesses into those monsters, which they intend to use to stop Team Green Fury. However, they need to learn how to use their new forms first.

In the Kingdom of Seltrozzo, Mariabel recalls her past as a corrupt noble from Earth, having died from old age. After being reborn in the Central World, she was given a special unique skill called Greed, which allows her to manipulate greed in others, though she doesn't use this power on Granville though. The two plan to bring peace to the world by conquering it. Back in Tempest, following issues with handling their avatars, Rimuru and his friends go to see Kurobe for new gear. They start training on how to properly handle their avatars in the Dungeon. Grad soon informs Rimuru about Team Green Fury's progress, and Raphael advices Rimuru to interfere with Ramiris's Mazecraft ability so he can learn about the team's stats. Once ready, the team proceed to stop Team Green Fury. The plan is successful. Team Green Fury leave following their loss. Meanwhile, Yuuki arranges a meeting with Mariabel. Since defeating Rimuru proves nearly impossible now to due to Veldora's presence, Mariabel comes with the idea to use Greed on Rimuru in hopes of controlling him. She also intends to use Yuuki for her own means, and begins her plan to lure Rimuru to Seltrozzo so she can set a trap for him. Meanwhile, Muese is murdered for his failures, leaving Souei shocked.

Rimuru and his friends continue to take on adventurers in the Dungeon using their avatars, which is attracting more challengers. Rimuru then gets a visitor: Frey, which makes Milim nervous since Frey is aware that she is still neglecting her duties. After Frey leaves with Milim, Shuna is also aware of Rimuru was doing this whole time. Grad arrives with a letter from the Council of the West, leading Rimuru to suspect that Team Green Fury were scouts sent by the Council. Meanwhile, Mariabel resumes her plans to destroying Tempest using the Council as pawns. The Council holds a meeting to decide whether they should ally with Tempest or not; Hinata is also attending the meeting. Eventually, the Council decide to let Tempest join them after all, but they also have concerns about the Eastern Empire and Veldora. Hinata leaves the meeting afterwards, but Elric, the first prince of Engrassia, and his knight Reiner, want to speak with her. Eric asks Hinata to serve as his bodyguard during the upcoming meeting with Rimuru to see if he is trustworthy or not, as he is still skeptical of the monster leader. Hinata refuses due to her allegiance with Tempest, warning him against antagonizing Rimuru. Elric did not take this rejection kindly. However, Hinata also suspects that the meeting was set up. Rimuru prepares to attend the meeting with the Council with Shuna, Benimaru, and Souei, though Shion is unhappy that she has to stay behind, until Rimuru explains that he's leaving her in charge of Tempest.

Rimuru and his subordinates arrive in Engrassia to join the Council of the West. They first take a tour of the place and start by buying new clothes, though Rimuru ends up getting kids' clothes by mistake. At a restaurant, they meet Hinata again. After casting a soundproof barrier, Hinata tell Rimuru more about the meeting and warns him that some of the nobles are opposing Rimuru or planning to use him for their own means, leading them to suspect that the Eastern Empire is taking action against the recent events. Rimuru asks Hinata to investigate Dwargon for a possible invasion route. Recalling Muese's death, they suspect that he has connections to the Western Nations. Meanwhile, Mariabel plans to sabotage Rimuru during the meeting so to prevent his alliance with the Western Nation and hopefully destroy him with the help of Johann, one of the Five Elders. Yuuki visits Mariabel and questions her motives. The next day, Rimuru visits the Council's headquarters where the Council members talk to him about the festival and the train that he was developing. As the meeting begins, the Council's chairman Lester names three rules that must be followed when joining the Council. Rimuru agrees with the conditions, but upon reading the results, Rimuru reacts with hostility.

It turns out the Council is attempting to take advantage of the new train, Tempest's weapons and fortune, and the Dungeon, which Rimuru takes as an act of slavery. Raphael senses that someone is manipulating the Council, so Rimuru removes the mental influence, but he wonders who was responsible for it; he does not suspect Yuuki. Elric arrives with Reiner, Team Green Fury and their leader Vent, and Gaiye, having been summoned here by Gaban, another one of the Five Elders, to deal with Rimuru against Lester's wishes. The rest of the Council weren't expecting this. Hinata, who was also in the meeting, is also displeased with this idea, but Elric reveals that he planned to take down and control Rimuru, demanding the Council to help him. Elric uses an Orb of Domination, the same thing that was used to control Milim (even though she wasn't really brainwashed); it cannot control Rimuru, but Elric doesn't know that. Elric attempts to force Rimuru to wear it, but the Council turns against him, leading to Gaban's plan being exposed by Rimuru. Elric's group refuse to give up, so Hinata takes on Reiner while Gaiye attempts to fight Rimuru, but Shuna decides to take him on instead. Hinata easily defeats Reiner and Shuna swiftly destroys Gaiye's holy sword before taking him down using her magic. Raphael senses Glenda attempting to kill Elric from a distance for his failures, which Rimuru stops at the last second. They suspect that someone is trying to frame Rimuru for murder as Reiner and Gaiye are arrested. Elric ends his conflict with Rimuru after seeing that he isn't evil, but also sees that Gaban is responsible for the whole thing. He doesn't have proof, but Aegil, the king of Engrassia and Elric's father, arrives and clears things up, forming an alliance with Rimuru while disciplining his son for his actions and having Gaban arrested. This worries Johann, who was also in the meeting. The Council decides to accept their allegiance with Rimuru after all, but with more peaceful matters. Meanwhile, Souei confronts Glenda following her failed assassination attempt.