The struggle between good and evil is another prevalent theme. The devil king represents evil in most cases, but the story may show that the line between good and evil is not always so clear. There could be 'good' characters with bad intentions and vice versa, and the devil king may have some positive aspects to their character that make the reader question the traditional view of good and evil.
Power and domination are common. The devil king is usually a very powerful figure, and the story often revolves around their power and how they use or lose it.
Redemption can also be a theme. Some devil king light novels explore the idea of the devil king trying to change their ways or make up for past misdeeds. For example, they might start to care about the people in their domain instead of just ruling with an iron fist. This can add a lot of depth to the story as we see the character grow and develop.
Morality. These novels often explore the grey areas between good and evil. Just because a character is a god doesn't necessarily mean they are good, and devils may not always be completely evil. This makes the readers question the traditional concepts of right and wrong. For instance, a devil might be acting out of self - preservation in a world where the gods are tyrannical.
Power struggle is a common theme. The devil princess may be vying for power within the devil realm or against other supernatural forces. Another theme is redemption. She might be trying to break free from the negative connotations of being a devil.
One common theme is the struggle between good and evil. Since angels are often associated with good and devils with evil, their interactions and the choices they make highlight this eternal struggle.
Power is likely to be a common theme. The 'flame devil dragon king' is probably very powerful, and the fanfic might explore how it uses or abuses that power.
Power and politics are often common themes. Since a king is involved, there are usually political power struggles in the background. Love and romance are also key, as it's about a proposal which implies a romantic relationship. And loyalty, as the characters around the king may have different levels of loyalty to him, which can impact the proposal and related events.
Power is a common theme. The undead king usually has great power and has to manage it. For example, in some novels, the undead king might be trying to expand his territory using his power.
Power and leadership are common themes. The main character, as a soldier king, usually has great power and is in a position of leadership.
One common theme is loyalty. King Dice's loyalty to the Devil is often explored, whether it's being tested or reaffirmed. For example, in many fanfictions, there are situations where King Dice has to choose between his own interests and remaining loyal to the Devil.
Power is a common theme. As a great demon king, characters often have to deal with the acquisition and proper use of great power. For example, in 'Overlord', the main character has to figure out how to use his overwhelming power in the new world.
A prevalent theme is redemption. Sometimes, the demon king may not be entirely evil, and there could be a chance for him to be redeemed, or the hero may have to struggle with his own dark side. Also, friendship and loyalty play a part. The hero often has comrades who support him, and the demon king may have his own followers. Their relationships within their respective groups are important aspects. In addition, the theme of sacrifice is often seen. The hero may have to sacrifice something precious to defeat the demon king or vice versa.