A single mommy in One Piece fanfiction could also be a marine. She might be struggling to balance her duties as a marine and raising her child alone. Maybe she gets assigned to a mission that involves an area where her child is in danger. She has to make tough decisions between following orders and protecting her family, and this inner conflict could be a major part of the story.
It can be unique by having the single mommy be a devil fruit user with a very unusual power. For example, a power that is related to motherly instincts like the ability to create a protective shield around her child at all times. This would add an interesting twist to the story and make her stand out in the One Piece world filled with all kinds of powers.
One plotline could be that the Avengers are accidentally transported to the One Piece world. They have to find a way back home while also getting involved in the local conflicts. For instance, they might help the Straw Hats against the World Government. Another could be that Thanos has also found his way into the One Piece world and is after the One Piece treasure for his own evil purposes, so the Avengers and the Straw Hats have to join forces to stop him.
Since I'm not sure about specific 'One Piece Wanda Lemon' fanfiction, but generally in One Piece fanfiction, a plotline could involve new adventures for the Straw Hat crew. Maybe Wanda is a new character who has some special abilities and joins the crew on a quest to find a new treasure. Or perhaps she has a connection to an existing villain in the One Piece world and the story unfolds around that conflict.
There could be a plotline where they get transported to a different dimension. In this new world, Zoro has to learn new sword techniques to fight the strange creatures. Sanji discovers new ingredients and has to adapt his cooking. Luffy befriends some of the locals and together they figure out a way to get back to their own world.
One possible plotline could be Arlong and Luffy having to team up against a common enemy in a very unlikely alliance. This would force them to put aside their differences and learn to work together.
One possible plotline could be Kyoya and Tamaki taking on the roles of'mommy and daddy' to help a new member of their group adjust. They could be teaching the newbie about their world, like how to act in certain situations and the rules to follow.
In some 'One Piece' pregnant fanfics, the plot could revolve around the idea of legacy. If a main character gets pregnant, it could be about the future of the pirate crew or the world of 'One Piece' in general. How will the child grow up? What kind of impact will the pregnancy have on the balance of power in the world? Maybe the unborn child has some sort of special power that is discovered during the pregnancy, and this leads to various factions trying to either protect or capture the mother and the child. There could also be a story about a character who was thought to be infertile getting pregnant, which could be a source of great joy and also potential danger as others may envy or want to harm the mother and child.
One plotline could be Voldemort falling in love with a pure - blood witch from an ancient family. He might see her as the perfect match to carry on his pure - blood legacy. He woos her with his power and promises of a new world order. However, she has a kind heart and tries to change him, which creates a lot of internal conflict for Voldemort.
One plot could be that Cedric is cursed by a dark wizard during the Triwizard Tournament. A kind - hearted witch from his own house, Hufflepuff, tries to break the curse. In the process of helping him, they develop a deep connection. As she uses her knowledge of ancient magic to fight the curse, Cedric sees her in a new light. They start to have feelings for each other as she nurses him back to health. Another idea is that Cedric falls in love with a time - traveler. The time - traveler is from the future and comes to Hogwarts for a mission. Cedric gets involved in her mission, and during their adventures, they fall in love. But there are complications as the time - traveler has to return to her own time eventually, and they have to figure out how to be together across time.
A possible plotline could start with Latias being curious about Ash after seeing him in a Pokemon battle. She disguises herself as a human and gets closer to Ash. They end up going on a quest together to find a rare Pokemon. During this quest, they face many difficulties, but their connection grows stronger. Ash realizes his feelings for Latias as she reveals her true form to him in a moment of danger, and from then on, their love story unfolds.