There is a wizard who is also an important character. He often helps the main swordsman with his magic powers, especially in difficult battles. And there is a female character, who is strong - willed and a great fighter herself. She has her own goals and sometimes clashes with the main character but also becomes his ally at crucial times.
In my opinion, the battles against powerful demons are really interesting. The detailed descriptions of the fight scenes, like the use of magic and sword skills, are quite thrilling.
The plot involves Rimuru's journey from being a rather weak (initially) slime to becoming a very powerful being. He meets many interesting characters. For example, there are the goblins he befriends early on. Rimuru helps them improve their living conditions. As the story progresses, he also has to deal with the threat of other more powerful monsters and even some human kingdoms that view his growing power with suspicion. In general, it's a story full of adventure, growth, and the forging of relationships in a magical and dangerous world.
The main character is Rimuru Tempest. He is a slime who has unique powers and a great deal of charisma. Another important character is Veldora, the storm dragon who befriends Rimuru. There is also Shizu, a human who has an impact on Rimuru's early development. And then there are characters like Benimaru, a powerful ogre who becomes one of Rimuru's loyal followers.