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.
The Tensura web novel follows the story of Rimuru Tempest. He starts as a normal salaryman in Japan but is reincarnated in a fantasy world as a slime. Rimuru then begins to build his own nation and gathers various powerful and unique beings around him. He also gets involved in many power struggles and battles against other strong entities in this new world.
In the Tensura Light Novel, the theme of adventure is quite significant. Rimuru embarks on numerous adventures, facing different challenges and foes. There is also the theme of adaptation. Rimuru has to adapt to his new form as a slime and the strange world he finds himself in. Additionally, the theme of loyalty is there, as his friends and followers remain loyal to him through thick and thin.