In nephilim books fiction, nephilim are often depicted as powerful beings. They usually possess superhuman strength, for example, being able to lift heavy objects or fight with great force.
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.
Well, the Nephilim true story is quite mysterious. According to some ancient texts, they were extraordinary beings. It's said that their existence was a sign of a time when there was an unusual mixing of the divine and the human. But really, we only have these texts to go on. There are different interpretations. Some believe they were a powerful race that had great strength and influence. Others think it was a way to describe a group that was different from the norm, perhaps with advanced knowledge or abilities. But again, it's all speculation based on limited information.
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.