Perhaps the Dragon King has some sort of prophecy about Harry. So, in order to fulfill this prophecy, Harry has to journey to the Dragon King's realm, learn their ways of magic, and bring back some sort of powerful artifact or knowledge that can help him in his fight against the dark forces in the wizarding world. This would involve him making new allies and facing new enemies in the Dragon King's world.
One possible plotline could be that Harry discovers he has a hidden heritage related to the Dragon King. Maybe his parents had some connection to the Dragon King's world that was kept secret, and now he has to figure out how to use this new - found knowledge and power to fight against Voldemort.
One possible plotline could be that Harry discovers he has the ability to communicate with dragon serpents. This newfound skill helps him in his fight against Voldemort. Maybe the dragon serpents know of a hidden weakness of Voldemort's that no one else does.
One possible plotline could be that Harry is cursed and slowly turns into a dragon. As he changes, he has to deal with the physical and mental challenges of this transformation. His friends would try to find a way to reverse the curse while Harry struggles to control his new instincts.
Perhaps there is a magical tournament in the wizarding world that is modeled after the jousts and challenges in King Arthur's court. Harry is forced to participate and as he does, he realizes that there are deeper connections between the values of the Arthurian era and the current state of the wizarding world. He then uses this knowledge to bring about positive change in the wizarding community.
Perhaps Harry discovers that he has basilisk blood in him. This could change his abilities and how others view him. He might face discrimination from some in the wizarding world who fear the basilisk's power, while others might see him as a potential weapon against Voldemort. The plot could revolve around Harry coming to terms with this new aspect of himself.
One possible plotline could be that Harry, as a cyborg, uses his mechanical abilities to enhance his magic. For example, he might have a built - in spell - enhancer in his robotic parts that allows him to cast more powerful spells. Another could be that he has to hide his cyborg nature from the wizarding world at first, fearing they will reject him, but then uses it to fight a new kind of dark force that is immune to normal magic.
One possible plotline could be that the wizarding world has its own version of cops. Harry Potter and his friends could join this force and use their magic to solve magical crimes that the regular Aurors can't handle. For example, they might deal with dark wizards who are using new and undetectable forms of dark magic.
A plotline could involve an Uchiha character from the Naruto world being sent to the Harry Potter universe. This Uchiha could befriend Harry and teach him some of the Uchiha techniques, like how to enhance his senses or use some basic ninjutsu. Harry, in turn, could introduce the Uchiha to magic. Together, they could face threats in the wizarding world, like a new dark wizard who is immune to normal magic but vulnerable to ninja techniques.
One possible plotline could be Harry using his newfound baron status to reform the wizarding world's social structure. He might try to bring more equality among pure - bloods, half - bloods, and Muggle - borns. Another could be him having to deal with the political intrigue that comes with being a baron, like rivalries with other noble wizarding families.
Maybe Harry, as a politician, has to deal with the aftermath of the war. He could be trying to unite different factions within the wizarding community that were divided during the battle against Voldemort. He might face opposition from traditionalist wizards who don't want to see the changes he is proposing, such as equal rights for house - elves or better integration of muggle - borns into the wizarding society. And he would have to use his charm and the respect he has earned from his heroic deeds to convince others to support his political agenda.
Well, perhaps there could be a plot where the virus is actually a dark magic - created plague. The Ministry of Magic is in chaos as they try to deal with it, and it's up to Hermione to research and find a solution using her vast knowledge of magic. Or maybe the virus is spreading among the Muggle - borns first, and Ron has to deal with his family's concerns while also trying to help his Muggle - born friends. There are many directions it could go depending on the creativity of the author.