Tanjiro Kamado is a main character. He is a determined demon slayer on a quest to find a cure for his sister Nezuko, who has been turned into a demon. Nezuko herself is also important as she retains some of her humanity despite being a demon.
The key features include its unique characters. The main characters like Tanjiro have distinct personalities and backstories that drive the plot. The story also has a richly detailed demon - slaying world with different types of demons and their powers.
Well, in 'kimetsu no yaiba the first novel', it probably focuses on the early days of the main characters. It could be about Tanjiro's journey as he first discovers the existence of demons and decides to become a demon slayer. It might also include his encounters with other important characters like Nezuko, and how their relationship develops in this different narrative format.