Well, it could be about Harry using his skills and magic knowledge to custom - create a super - powered Firebolt. Maybe he adds some unique enchantments to it for speed or stealth.
Harry is the main one, but other characters could be involved in different ways. Neville could accidentally stumble upon Harry's secret project and, in his clumsy but kind - hearted way, end up helping. Luna Lovegood might offer some out - of - the - box ideas with her unique perspective on magic. And Dumbledore, with his vast knowledge and wisdom, could be a guiding figure in the background, giving Harry some cryptic advice that helps him in the creation of the Firebolt.
One possible reason could be for speed. The Firebolt is known for its incredible speed in the Harry Potter series, and Harry might need it for faster travel between Hogwarts and other places, or for Quidditch matches to outrun his opponents more easily.
The plot could start with Harry finding an ancient Jedi artifact during one of his adventures. This leads him to become curious about lightsabers. He then uses his magic knowledge to try and replicate it. Along the way, he might face opposition from some in the wizarding world who think it's too dangerous or against wizarding traditions. But Harry, being the hero he is, persists. Eventually, he creates a lightsaber and uses it to defeat a new, powerful dark wizard who has emerged, using both his wizarding skills and his new lightsaber skills.
In a fanfiction where Harry Potter creates a virus, perhaps it's a virus that affects magic itself. The virus could spread through spells and start to corrupt the very essence of magic. Harry, realizing the severity, might then have to team up with his old friends like Hermione and Ron. They would search for ancient magic or rare potions to counteract the virus before it destroys the entire magical ecosystem.
In a 'Harry Potter creates a shelter' fanfiction, perhaps Harry uses his magic to create a shelter in the Forbidden Forest. He might use spells like Protego Totalum to make it safe from dark creatures. It could be a place where he hides his friends during a dangerous time at Hogwarts, like when Voldemort's forces are on the prowl.
One possible plot could be that Harry, after defeating Voldemort, decides to create a kingdom where magic and non - magic folk can live together in harmony. He uses his knowledge of magic and the respect he has gained to build a new society with its own set of laws and governance that are fair to all. For example, he could create schools that teach both magic and Muggle subjects to promote understanding between the two worlds.
One idea could be that Harry discovers a hidden spellbook in the Room of Requirement that has ancient alchemical knowledge. He uses this to recreate the Philosophers Stone, but with a twist. Maybe he wants to use it to heal all the students who were injured during the Battle of Hogwarts. Another idea is that Harry creates the Stone in secret and uses it to gain more power to fight against the remaining Death Eaters. However, he soon realizes that power from the Stone comes with a great price and he has to make a difficult choice.
Well, perhaps Harry Potter, using his magic, accidentally creates the world of Remnant from RWBY. He might then have to deal with the new and strange creatures and powers there, while also trying to find a way to get back to his own world.
One possibility is that Harry Potter, using his knowledge of magic and experiences, decides to create a school for mutants. He could use spells to protect the school from the outside world and those who might fear the mutants. He might also teach the mutants how to control their powers, just as he learned to control his magic at Hogwarts.
Maybe he loves the idea of the Firebolt in the fanfiction. It could be that the stories expand on his experiences with the Firebolt in a really exciting way.