Power and control are often common themes. Villains usually strive for power over others, whether it's in a small community or a large kingdom. Another theme could be revenge. Maybe the villain has been wronged in the past and is seeking retribution in extreme ways.
Well, power is often a theme. The hero and the villain might be vying for power, whether it's political, magical or just over a group of people. Also, the theme of sacrifice can be present. The hero may have to sacrifice something dear to defeat the villain.
The exploration of good and evil is also a big theme. In 'Grendel', we see that the line between good and evil is not so clear. Grendel is not simply a villain, and through his story, we question what truly makes a hero or a villain. Often, these novels also deal with themes of social outcast. The characters start as outcasts, like the wrongly imprisoned Edmond Dantes, and they rise above their circumstances to become heroes.
A third theme could be transformation. The villain may transform into a better version of themselves. In the case of 'Twilight', Edward tries to control his vampiric instincts because of his love for Bella. His 'villainous' side related to his blood - thirsty nature is subdued by his love for her, showing how the hero's love can bring about change in the villain.
One common theme is redemption. Since the baby is related to a villain, there is often a journey towards redeeming the family name or breaking free from the villain's shadow. Another theme is growth against all odds. The baby has to grow up in a world that may not be friendly, so it has to overcome many difficulties. Also, the exploration of identity is a theme. The baby has to figure out if it will follow in the villain's footsteps or create its own path.
One common theme could be the struggle between good and evil. The protagonist is 'caught' by the villain, so there's likely a fight for survival or freedom. Another theme might be redemption, if the villain has a chance to change. Also, themes of power and powerlessness can be present as the protagonist is in the clutches of the villain.
One common theme is the corruption of the soul. As the villain gives in to their dark side, their inner self becomes tainted. For example, in 'Crime and Punishment', Raskolnikov's decision to commit murder starts his journey into his own dark side, and we see his moral and mental corruption.
One common theme is the struggle between good and evil. The hero represents all that is good, like justice and kindness, while the villain stands for greed, power - hunger or malice. Another theme can be redemption. Sometimes the villain has a chance to turn good, or the hero might face a moral dilemma that tests his own 'hero - ness'. Also, the theme of sacrifice often comes up, where the hero might have to give up something precious to defeat the villain.
In 'villain deku fanfiction', a frequent theme is the subversion of expectations. Since Deku was initially seen as a pure - hearted hero, seeing him as a villain completely turns that on its head. Another theme is the power struggle. He has to fight against the heroes he once called allies. The theme of identity crisis is also there. He is no longer the Deku everyone knew, and he has to redefine himself as a villain. There's also the theme of the dark side of heroism, showing that the very qualities that could have made him a great hero can be twisted into making him a terrifying villain.
One common theme is power corruption. Often, Percy in these fanfictions becomes a villain due to his pursuit of too much power. Another theme is revenge. He might be wronged in some way and then seek vengeance in a villainous manner. And there's also the theme of identity crisis. As he turns into a villain, he may struggle with who he really is.
Isolation is also a theme. Naruto has always craved acceptance. If he is pushed into a corner and isolated completely, he may turn to villainy. He might think that if the world won't accept him as he is, he'll make the world fear him. This theme can explore the psychological effects of loneliness and rejection on a character as powerful as Naruto.