A possible plotline could be that the dragon is lost and Harry helps it find its way home. Along the way, they form a bond and the dragon becomes Harry's ally. Harry could use the dragon's abilities, like flying on its back, to gain an advantage in his fight against the forces of evil.
Another plotline might be that the dragon is sent by a powerful magical being to test Harry. The dragon challenges Harry in various ways, such as by setting up magical trials. Through these trials, Harry grows in his magical abilities and wisdom.
One possible plotline could be that Harry, as a submissive dragon, is forced to follow the commands of a more powerful dragon or wizard. He might struggle against this submissive role and try to break free.
One possible plotline is that the dragon helps Harry discover a hidden magical place. Since dragons have a strong sense of magic, it could lead Harry to a place full of ancient spells or powerful artifacts.
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.
One possible plotline could be the dragon of darkness being hunted by a group of adventurers who see it as a threat to their world. Another could be the dragon trying to find a way to overcome its own dark nature.
One possible plotline could be Harry struggling to keep up with his magical training due to his anemia. He might have to find alternative ways to gain strength for spells.
One possible plotline could be Harry struggling to accept hugs or physical contact from his friends, causing misunderstandings among them.
One possible plotline could be that Harry somehow gets transported to the world where Izaya exists and they form an unlikely alliance. Maybe they team up to solve a mystery that is plaguing both their worlds.
A possible plotline could involve Harry being transported to the world of Alduin and being mistaken for Alduin at first. As he tries to figure out what's going on, he has to learn about Alduin's powers and how to control them. Meanwhile, the real Alduin might be on the loose and Harry has to either stop him or find a way to co - exist with him. There could also be a plot where Harry uses his knowledge from the wizarding world to bring about new changes in the world of Alduin, which might be met with resistance or acceptance from the natives of that world.