The concept of Harry Potter as captain of a starship in fanfiction is really interesting. Imagine he has a wand - powered engine or something. His knowledge of magic could be used to create new technologies on the starship. He might also encounter different species of magical beings from other planets. His ability to think on his feet, which he developed during his years at Hogwarts fighting Voldemort, would serve him well when making quick decisions during starship crises, like when they're caught in a black hole's gravitational pull or facing a surprise attack from a space pirate fleet.
The plot could involve Harry using his knowledge of spells and potions to create a unique starship. He could also recruit his wizard friends to help him. For example, Hermione could use her vast knowledge to research the best magical elements to incorporate into the ship's design, while Ron could provide his loyalty and physical strength for the more labor - intensive parts of the construction. And they might face challenges from the wizarding world, like the Ministry of Magic trying to stop them for fear of revealing magic to the Muggle world through their starship adventure.
He would become more of a space - faring leader. His focus would shift from the wizarding world on Earth to the cosmos. He'd probably be more open - minded about different cultures and species, just as he was about different wizarding houses at Hogwarts.
It could be about Harry Potter somehow being transported to Neverland and taking on the role of Captain Hook. Maybe he uses his magic to rule the pirates in a different way than Hook did.
The Death Eaters could be the antagonists. Even though Voldemort is gone, some of his followers might not want Harry to succeed in building a starship as they fear it could bring more power to Harry and his friends, and they still hold grudges against him.
It could work if the characters from both universes were to cross over. Imagine Harry Potter and his friends joining the Mobile Infantry. Harry's leadership skills and his ability to think on his feet, which he developed while fighting against Voldemort, could be very useful in the battles against the bugs. Hermione's vast knowledge of magic could be applied to find new ways to combat the alien threat. Ron's loyalty and courage would also be valuable assets. The different cultures of the two universes would also create interesting clashes and collaborations.
Perhaps Harry discovers that there are dark wizards hiding among the pirates. As a pirate captain, he has to not only find the lost treasures but also stop these dark wizards from using pirate ships to spread evil. He would use his knowledge of magic and his leadership skills to build a crew that can take on these challenges.
Well, in some Harry Potter starship fanfiction, there might be the idea of using Patronuses as a form of energy source for the starship. Since Patronuses are powerful positive magical manifestations, they could potentially power up the ship's engines. Also, there could be a story where the starship has to travel through different magical dimensions, like the ones that might be related to the Forbidden Forest's hidden areas, and the crew has to use their knowledge of Hogwarts magic to survive.
It could be a story where Fem Harry Potter discovers Captain Marvel's story through some magical means, like a magical book or a wizarding TV (if there was such a thing in the Potterverse). And she becomes a huge fan. This could lead to her trying to bring some of Captain Marvel's values to Hogwarts. Like promoting more equality between genders in magic, since Captain Marvel is a symbol of female empowerment. She could start a club or something at Hogwarts dedicated to the study of strong female heroes, with Captain Marvel as the main inspiration.
Well, one possible plot could be that Harry discovers his true heritage as Captain Hook's son. This might lead to him having some unexpected pirate - like abilities. He could have a natural skill with a sword, for example. And perhaps he would be drawn to the sea more than he is to Hogwarts. He might struggle to fit into both the wizarding world and the pirate world he's suddenly connected to.
In a fanfiction of Harry Potter, Captain Marvel and lemon, it could be that lemon is a new spell or potion ingredient in the wizarding world. Captain Marvel somehow gets transported there. She's confused at first but quickly adapts. Harry Potter and his friends are intrigued by her powers. They all work together to create a new potion using the lemon ingredient that can give temporary superpowers to wizards. This leads to a series of adventures as they try to keep the potion's recipe safe from dark wizards.