Perhaps a plot where the Futa character has a special power related to the sea, and Female Luffy, with her dream of becoming Pirate King, needs that power to access a hidden island full of treasures. Their journey together is filled with adventures, like battling new sea monsters and dealing with other pirate crews who also want the power.
A possible plot could be that Margaret gets into trouble with a powerful pirate group. Luffy comes to her rescue and then they decide to travel together for a while. During this time, Margaret learns about Luffy's dreams and they support each other in achieving their individual goals. They might also encounter some strange islands and have to work together to survive on them.
One idea could be that the werewolf futa is from a powerful werewolf clan and the girl is a human who stumbles upon their territory. The werewolf futa is initially protective of her clan but gradually falls for the girl's kind nature. Another could be a story where the girl is a witch and she uses her magic to help the werewolf futa control her more wild instincts during full moons.
One possible plot idea could be that in an alternate universe, Rem and Ram have a unique relationship where they face challenges together in a world that is more accepting of different genders and identities. Another could be a story where they discover a magical item that causes some changes in their physical forms and they have to deal with the consequences while still maintaining their strong bond. A third idea might be a journey they take together where they meet different characters who have different views on their relationship, and they grow stronger as a couple through these encounters.
One idea could be a story where Dva and Tracer are in a parallel universe where they are part of a racing team together. They start off as rivals in the team but gradually develop a deep friendship that could potentially turn into something more. Another plot could involve them teaming up to save their city from a new kind of digital threat. They use their unique skills, Dva's mech piloting and Tracer's time - jumping abilities, to outwit the enemy.
A plot could revolve around a self - insert being transported back in time and having to gather the Infinity Stones before Thanos does. Along the way, they form unexpected alliances with the Avengers from different timelines. They might start with finding the Space Stone and use it to travel between planets in search of the others.
One idea could be a story where Luffy and Sanji get separated from the crew during a battle and have to rely on each other to survive on a strange island. They could discover new types of food that only Sanji can cook and Luffy can't resist, leading to some comical and heartwarming moments.
The character dynamics are also special. Luffy's boundless energy and positive attitude contrast with Wanda's often more brooding and powerful presence. In many luffy x wanda fanfics, we see how Luffy can break through Wanda's guarded exterior and bring out a more adventurous side of her. For example, in some stories, Luffy convinces Wanda to join him on a wild treasure hunt, which is something she would never have considered in her normal Marvel - based storylines.
One idea could be that the OC is a powerful mage from a far - off land who comes to Arendelle during a time of new danger. The OC meets Elsa and they initially have a bit of a clash due to their different ways of using magic. But as they face the new threat together, they start to understand and respect each other more. Eventually, they combine their magical powers to save Arendelle and in the process, form a deep friendship or even more.
For a Luffy Gear 5 fanfic, you could have a plot where Luffy's Gear 5 form is somehow corrupted by a dark force. He starts to lose control of his actions and becomes a danger to his friends. His crew has to find a way to purify his Gear 5 power. Another interesting idea is that Luffy discovers that Gear 5 has a hidden ability that allows him to travel through time briefly. He uses this ability to go back and change a crucial event in the past that has far - reaching consequences for the present. This could lead to a whole new set of adventures and challenges for Luffy and his crew.
One idea could be that Dragon discovers Luffy's true potential during a battle against a common enemy. Maybe Dragon secretly aids Luffy without him knowing, guiding the wind or weather to give Luffy an advantage. This would add an interesting layer of mystery to their relationship within the fanfic.