Rimuru's relationships with each of the Demon Lords are different between each one
Milim Nava: She and Rimuru became close friends over the course of her two week stay in Tempest. Shortly after her arrival, Rimuru gave her "dragon knuckles" to inhibit her power so she wouldn't hurt or kill any of his citizens accidentally and since then, she rarely takes them off due to her fondness of Rimuru though when Rimuru made her do so while she was eating, Milim sulked for the entire day. They have become so close to the point that she was willing to pretend to be under Clayman's control in order to expose his plot and help Rimuru. This close friendship can be assumed to give birth to "love" within Milim in regards of her feelings towards Rimuru.</nowiki>
Ramiris: Their relationship started off rocklily due to Rimuru destroyed her golem and looking down on her due to her cheeky attitude to him. Nevertheless, Rimuru still made a new golem for her, in the form of Beretta, for compensation. Because of that, she felt gratitude and became friendly with him, to the point that she warned Tempest of its possible impending doom due to Clayman's plan at the Walpurgis. She then joined Tempest and moved her Labyrinth to next to it. After that,Rimuru employed her to manage the Labyrinth as an attraction for Tempest and they had fun creating the Labyrinth together. Along with Veldora and Milim, they also had fun together using the avatars created by Rimuru to enjoy the Labyrinth. Ramiris developed many researches that would benefit Tempest such as the Demon dolls for the Black Corps.
Karion: Karion and Rimuru get along with each other, especially when they both have the experience to have to deal with Milim's antics and childish behaviours.
Frey: Frey and Rimuru get along with each other, especially when they both have the experience to have to deal with Milim's antics and childish behaviors. In addition, Rimuru respects her to some degree as she is among the few people who can rein in Milim and force her to be obidient.
Dino: Rimuru and Dino can be said to be on friendly terms with each other. As Dino is chased out of Dagrule's place and then told by Guy to go to Tempest, he is employed by Rimuru as Ramiris's assistant. Even though he's been discovered to be a spy and an enemy there is no negative feelings towards each other
Leon Cromwell: At first, Leon held no interest in Rimuru while Rimuru disliked Leon to the extreme due to Shizue. Upon learning his relationship with Chloe and his intention, their relationship underwent some changes with Leon recognizes Rimuru and Rimuru respects him to some degree though still dislikes him. They eventually form an alliance to rescue Chloe.
Dagrule: Rimuru and Dagrule can be said to be on good terms with each other as they converse casually and pleasantly with each other during the event of Walpurgis Banquet. Dagrule trusts Rimuru enough to send his sons over to Tempest to learn.
Ruminas Valentine: Ruminas disliked Rimuru at first due to his connection with Veldora. However, after witnessing Rimuru's "performance" at the Walpurgis, she began to take an interest in him. Later on, as they both share the common goal of saving Chloe, they allied with each other in the Saint-Demon Alliance. Occasionally, Ruminas' haughty attitude towards him look like that of a tsundere, as noted by Rimuru.
Guy Crimson: Ever since hearing the rumour of Rimuru, Guy had begun to take an interest in the Slime that managed to become a Demon Lord. After seeing him eye to eye, Guy's interest in Rimuru grew even more knowing that he too possessed Ultimate Skills. For a while, Guy suspected Rimuru due to the fact that Tempest suffer no casualty in war with the Eastern Empire, Guy's enemy, and the awakening of several True Demon Lords in Tempest. Thanks to Rimuru's explanation, the misunderstanding is solved, and the two became friendly to each other again, with Rimuru eventually help Guy evolve his 2 subordinates and teach them how to make cakes for Guy.