Another angle could be a romantic relationship between them. It would be interesting to see how their relationship develops, considering their different backgrounds. For example, Robin's past with the Straw Hats and Hancock's role as a Shichibukai. Their relationship could bring out new sides of their characters that we haven't seen before in the original story.
Redemption could be an unexpected theme. If one of them has made mistakes in the past, the other could help them find redemption. For instance, if Hancock has some actions she regrets due to her pride, Robin with her calm and wise nature could guide her towards a path of self - forgiveness.
One idea could be that the OC is a new pirate who joins the Straw Hats. Over time, they develop a special bond with Nico Robin due to their shared interest in ancient history. Meanwhile, during an encounter with Boa Hancock, the OC manages to gain her respect in an unexpected way, like saving her from a new threat in the Grand Line. This could lead to a complex love triangle where the OC has to navigate their feelings for both strong - willed women.
First, you need to develop your OC well. Give them a unique backstory, personality traits, and goals. For example, if your OC is a chef, their cooking could be a way to bond with Nico Robin (maybe she loves a certain dish) and Boa Hancock (by impressing her with a special recipe). Also, understand the personalities of Robin and Hancock. Robin is calm, intelligent, and has a dark past, while Hancock is proud, strong, and has her own insecurities. Incorporate these into how your OC interacts with them.
Another interesting one is 'Love on the Grand Line: Hancock and Luffy'. It delves deep into the idea of how their relationship could develop. It has some great character development for both of them and shows how their different personalities could come together in a romantic relationship.
One common theme is the clash and then the fusion of different cultures. Naruto is from a ninja - based world with its own set of values and traditions, while Hancock is from the world of pirates in One Piece with the unique Kuja tribe culture.
Well, 'A New Alliance: Naruto and Hancock' is also a great one. In this fanfiction, their relationship starts with a misunderstanding which later turns into a strong alliance. They learn from each other's skills. Naruto shows Hancock some of his ninja techniques, and Hancock teaches Naruto about the ways of the Kuja tribe. It's really exciting to see how their different cultures blend in the story.
One common theme is the power dynamic. Boa Hancock is a very powerful character, so exploring how that power interacts with the reader character, whether it's the reader being protected or the two characters having a more equal relationship despite her power, is often seen. Another theme is the concept of love at first sight, which is related to Hancock's character trait of falling for Luffy quickly in the original story.
In fanfiction, Boa Hancock is often depicted as still being extremely beautiful and powerful. Her love for Luffy may be further explored, with different scenarios of how she might express it. She could also be shown as having more complex relationships with her sisters, perhaps mending some past rifts or facing new challenges together.
Well, a fanfiction involving Naruto and Boa Hancock could be really interesting. It might explore how their different worlds collide. Naruto, from a world of ninjas, and Boa Hancock from the One Piece world. Maybe in the fanfic, Naruto could be on a journey that somehow leads him to Hancock's island. And they could form an unlikely alliance against a common enemy.