Power dynamics is also a common theme. For example, one person may have more power in the relationship, either socially or financially, and use it to manipulate the other. This can lead to a very cruel situation for the less powerful character.
Common themes often include unrequited love. One character may love another deeply, but that love is not returned, causing great pain. Another theme could be betrayal. A character might be betrayed by their lover, which adds to the 'cruel' aspect.
One common theme is the power struggle within relationships. In Chinese novels, power dynamics can often play a cruel role in romance. For instance, family status and wealth can create barriers or cause manipulation in love stories.
Misunderstanding is a big theme. Usually, the cruel husband's actions are misinterpreted by the heroine and the readers at first. There's also the theme of hidden vulnerability. Most of these cruel husbands are not truly evil but are hiding some sort of pain or insecurity. In 'The Duke's Dark Secret', the duke's cruel facade is hiding his fear of abandonment, which is a common trope in such novels.
Common themes in 'cruel Snape fanfiction' include the exaggeration of his negative traits from the original books. His bitterness towards James Potter, for example, can be magnified. Another theme is the abuse of authority. As a teacher, his power can be misused in a cruel fashion towards the students. There's also the theme of self - loathing. His cruel actions might be a way of dealing with his own self - hatred, perhaps taking it out on those around him. This can make for some interesting, if rather dark, character studies in fanfiction.
Social differences often play a role. When two lovers are from different social strata, like in 'Romeo and Juliet' (which can be seen as a cruel love story due to the family feud and social barriers), society can be cruel to their love, preventing them from being together easily.
One common theme is betrayal. Like Naruto being betrayed by his comrades or mentors, which adds a cruel twist to his story. Another is isolation, where he is left all alone in the world of ninjas.
Love and sacrifice might be one of the main themes. Often in BL novels, the characters are willing to sacrifice a great deal for their loved ones.
Redemption is a theme that shows up in 'Cruel Summer' fanfics. There are characters who made mistakes in the original story, and fanfic writers often write about their journey towards redemption, how they try to make up for what they've done and how it affects their relationships with other characters. It gives the characters more depth and allows for different interpretations of the story.
Betrayal is a common theme. One partner may deceive the other for personal gain, like in the story where the boy used the girl for her wealth. Another theme is control, as seen when a jealous partner tries to dominate the other's life. And of course, unrequited love can also turn cruel when one person's feelings are constantly being toyed with.
The theme of unforeseen consequences is quite common. Naruto's actions, which are usually done with good intentions, lead to bad outcomes. For example, if his attempt to make peace between two clans actually results in a greater war. This is a cruel irony because his positive actions have the opposite effect. And there could be a theme of lost innocence, where Naruto's naivete and positive outlook are shattered by a cruel reality that he never expected.
One common theme is the struggle for power within the marriage. The cruel husband often tries to dominate his wife, which creates a power imbalance. Another theme is the emotional and psychological abuse that the wife endures.