Shizu is another important character. She has a connection to Rimuru's past life in a way. Her story arc is sad but also important for Rimuru's development. She was a powerful adventurer who had a special power within her, and Rimuru inherits some of her abilities after she passes away.
Shion is also a main character. She is an ogre and one of Rimuru's first followers. She is extremely loyal to Rimuru and is very strong. Her cooking, although often described as horrible, is a running gag in the story. Then there's Benimaru, a kijin. He is a very skilled fighter and strategist, and he plays a crucial role in Rimuru's kingdom - building efforts.
Veldora is an important character. He is a powerful dragon who becomes Rimuru's friend and ally. His presence adds a lot of power and mystery to the story.
The unique concept of being reincarnated as a slime is really interesting. It allows for a fresh take on the isekai genre. Also, the way the slime, Rimuru, builds his own community and kingdom is engaging.
Well, the themes include adaptation. Since he's suddenly in a new form and world, he has to adapt. Leadership is also there. As he gains power, he starts leading others. And there's a sense of exploration as he discovers new places and cultures in the world he's been reincarnated into.
One of the main plot points is Rimuru's reincarnation as a slime. He starts from a weak state but gradually grows in power. Another is his encounter and interactions with various races in the new world, like the goblins and dwarves. He also has to deal with political situations and power struggles within the different kingdoms.
Rimuru is definitely one of the most interesting characters. His transformation from a normal person to a slime and then to a powerful leader is fascinating. Veldora is also interesting. He is a powerful dragon trapped in Rimuru's stomach for a while and his interactions with Rimuru are quite humorous.
One interesting plot point is Rimuru's evolution. He starts as a simple slime but gradually gains various abilities and forms, which is really exciting.