One common theme is friendship. Often, the female characters and Marco develop a strong bond of friendship that helps them through difficult situations. For example, they might rely on each other during battles or when solving mysteries.
In general, it might feature unique character dynamics. Since it involves a futa (a character with both male and female sexual characteristics) and female Marco, there could be complex power dynamics and relationship exploration. But this is a very niche and often not mainstream type of fanfiction.
Star would be a likely candidate to rescue Marco. She has strong magical abilities and a deep friendship with Marco. She would stop at nothing to find him and bring him back safely.
There is also a fanfiction called 'The Female's Bond with Marco'. In this story, a female character forms a deep emotional bond with Marco as they face various hardships together. The author does a great job in depicting their relationship growth through different events.
A frequent theme is the exploration of jealousy and competition among the female characters in the harem. They might compete for the Marco Man's attention. Also, the journey of the Marco Man in dealing with multiple romantic interests and how he manages to balance or choose between them is a common aspect in such fanfictions. Usually, there is also a theme of adventure or a common goal that the group (Marco Man and the females) work towards, which helps to bond them together. This can range from fighting a common enemy to exploring a new world. It gives a reason for the harem to exist beyond just the romantic aspect.
There are indeed. Some fanfictions might focus on their adventures together in a new storyline that deviates from the original manga. Others could explore their relationship in a more emotional and character - development - centric way. It really depends on what you're interested in.
One common theme is adventure. They might go on new quests together. Another could be friendship that slowly develops into something more. And sometimes, there's the theme of protecting each other in dangerous situations.
You can also write about their emotional interactions. Maybe Luffy has a moment of self - doubt during their journey, and Marco, being the older and more experienced one, offers words of encouragement. He could share some of his own past experiences of facing difficulties. In return, Luffy's positive energy and unwavering belief in her goals could inspire Marco to look at things from a different perspective. This kind of mutual influence can be a great part of their character interactions.
One plot idea could be that the female Luffy is on an adventure and she meets Marco. They form an unlikely alliance to fight against a common enemy. Maybe a powerful pirate group that is threatening the safety of an island. Along the way, they learn from each other's skills and fighting styles.