One character that would make for an interesting pairing with Doflamingo in a crossover fanfiction is Zoro. Zoro's strong sense of justice and his skills as a swordsman would clash with Doflamingo's devious ways. They could have epic sword battles, and Zoro might be the one to cut through Doflamingo's strings, both literally and metaphorically. Also, Nami could be paired with Doflamingo. Nami's intelligence and ability to manipulate situations for her own gain, although in a more positive way compared to Doflamingo, could lead to some really interesting interactions. She could try to outwit him in a game of wits.
A great Corazon Doflamingo fanfic could be one that delves into his relationship with his family members other than Law. Maybe it shows how his relationship with his brother was like before things went sour. It could also explore his connection with his father and how that influenced his view of the world. Fanfics like these can add more layers to his already complex character.
Another plot could revolve around an OC who is a former victim of Doflamingo's cruel rule. This OC could be on a quest for revenge. They might start by gathering allies who were also affected by Doflamingo and then plan a elaborate scheme to take him down. Along the way, they could face many challenges and obstacles set by Doflamingo and his loyal followers.
One idea could be an OC who is a spy sent to infiltrate Doflamingo's organization. This OC could have a hidden past that slowly gets revealed as they gain Doflamingo's trust. Another idea is an OC with a special power that Doflamingo wants to control or use for his own evil plans. For example, the OC might be able to manipulate time in a small area, which could be a great asset in battles or heists.
One interesting aspect is the clash of different power systems. Naruto has its chakra - based powers like ninjutsu and bijuu powers, while Doflamingo has his string - based devil fruit abilities in One Piece. When combined in fanfiction, it creates unique battle scenarios. For example, seeing how Naruto's Rasengan would interact with Doflamingo's string attacks.
A good doflamingo x luffy fanfiction might be one where Doflamingo has a change of heart after seeing Luffy's unwavering determination. Luffy, in turn, tries to show Doflamingo that there is a different path than the one he has chosen. It could explore how their relationship evolves from pure antagonism to something more complex. Maybe in this story, they end up having to protect a group of people together, and through that experience, they form an unlikely bond.
One possible plot could be that Doflamingo somehow ends up in the RWBY world. He might initially try to take over, using his strings to manipulate the Grimm. But the RWBY team discovers his true nature and battles him. Ruby could use her speed to avoid his string attacks while Weiss uses her glyphs to counter his powers.
The contrast between their characters. Doflamingo is this power - hungry and somewhat cruel character, while Corazon is more empathetic. Their relationship is a mix of loyalty and conflict, which makes for great storytelling in fanfiction.
One idea could be a story where Crocodile and Doflamingo have to team up against a common enemy that threatens their own interests in the New World. Maybe a new and powerful pirate crew that is disrupting their business operations. Another plot could involve a past encounter they had that changed their relationship, like a time when they were both rookies and something happened that led to a grudging respect for each other.
A possible plot could be set in an alternate universe where Doflamingo is not a villain from the start. He and Nami meet on an island where they both have a common goal, like finding a rare treasure. As they search for it, they start to bond over their shared love for adventure and discovery, and a romantic relationship begins to form between them.