The villainess herself is often a popular character as readers are interested in her journey from being 'bad' to potentially 'good'. The male lead, who is usually involved in the villainess's romantic arc, is also popular.
One common theme is the transformation of the villainess character. Usually, she starts as a disliked or misunderstood figure but gradually changes for the better. Another theme could be romance. Often, there is a love interest involved that helps in the character's development.
The 'demon king retry web novel' could potentially be about a demon king who gets a second chance at something. It might tell the story of his past mistakes and how he plans to rectify them in this new attempt. There could be a complex world - building aspect with different races, magic systems, and political intrigues that the demon king has to navigate through in his retry.
I'm not entirely sure as I haven't read it in full. But generally, it might be about a villainess who tames a beast. This could involve a story of power dynamics, where the villainess has to use her wits and charm to subdue the beast, perhaps in a fantasy world filled with magic and adventure.
Often as extremely powerful. They have great magic or combat abilities. For example, in many novels, the Demon King can destroy cities with a single spell.
Another common main character could be a hero who is trying to oppose the great demon king. This hero may have special powers or skills that are meant to counter the demon king's tyranny. For example, they might possess holy magic or be a master swordsman. They play a crucial role in the story's conflict and development.
There is also 'Release That Witch'. While not strictly about a 'great demon king' in the traditional sense, it has elements of powerful magic and a protagonist who rises to great power, much like how a demon king would be in a web novel. The world - building and character development in this novel are quite engaging.
Since I haven't read it, I can't say for sure. But it's likely that the villainess herself is a main character. And of course, the beast she tames would also be a key character.
Another theme might be subverting traditional storytelling. By favoring the villainess, it goes against the normal narrative where the heroines are always the 'good' ones. This can lead to exploring different moral and ethical concepts.
One popular Demon King web novel could be 'Overlord'. In this novel, the main character is transported into a game world as a powerful Demon King - like entity. He has to navigate this new world with his in - game powers and minions.