Common themes might include the exploration of their pasts. Maybe there are some events in their pasts that are not fully explored in the original story but are delved into in the fanfiction. Also, the theme of loyalty and betrayal could be present. Given their complex relationship, whether they stay true to their own goals or betray each other for different reasons can be a big part of the story. And of course, there could be themes related to their individual quests for justice or power, and how these intersect with their relationship in the fanfiction.
One common theme could be power struggle. Doflamingo is a very powerful character and Law also has his own strength. In fanfiction, this power play between them can be a central theme. Another could be the idea of redemption or corruption. Depending on how the story is written, one character might influence the other in terms of moral standing.
Power dynamics is a very common theme. Given that both Law and Doflamingo are powerful characters in their own right, fanfictions often explore how they interact in terms of power. For example, who has the upper hand in different situations.
Power dynamics is a common theme. Doflamingo is a very powerful and manipulative character, and Law has his own set of skills and goals. Their interactions often involve a struggle for power or influence over situations or other characters.
I'm not really into this kind of fanfiction much. But generally, in such fanfictions, the relationship between Doflamingo and Law might be explored in a very different way from the original story. Maybe it focuses on their power dynamics and how they interact with each other in a more personal or emotional level.
Power dynamics is a very common theme. Doflamingo is a powerful character, so when paired with an OC, their relationship often involves struggles for control or mutual respect based on power. For example, in many stories, the OC has to find a way to hold their own against Doflamingo's authority.
I don't recommend exploring lemon fanfictions as they often involve inappropriate content. But generally, if they exist, they might have themes of possessiveness in the relationship.
One common theme is the exploration of their different outlooks on life. Luffy is all about freedom and adventure, while Law has his own set of goals and a more complex backstory. Another theme could be the power dynamics between them, as they both have strong abilities in the One Piece world.
One common theme could be the exploration of their relationship in a more intimate and passionate way, which is what the 'lemon' aspect often implies.
Power is a very common theme. Since Doflamingo is a powerful character, many fanfictions explore how he uses or abuses his power. Another theme is redemption. Some writers like to imagine if he could be redeemed or not.
One common theme is power dynamics. Doflamingo is a very powerful character in One Piece, so how that power affects the relationship with the reader is often explored. For example, in some fanfics, the reader might be in a position of weakness at first and gradually gain power or influence within the relationship.
One common theme could be the clash of their personalities. Luffyko's more carefree and adventurous nature against Doflamingo's more calculating and menacing side. This contrast can create interesting dynamics in the fanfic.