One idea could be that Harry Potter, as the Master of Death, somehow gets transported to the Ouran High School world. He could use his magical abilities in unique ways there, like using the Invisibility Cloak to play pranks on the Host Club. Maybe he'd also share his experiences with death and resurrection with the Ouran characters, leading to some deep philosophical discussions.
A plot could also revolve around Harry going back in time to the origin of the Master of Death legend. He discovers secrets about how the power was first created and used. Along the way, he meets his ancestors or other powerful wizards from the past. This could change his understanding of his own power and his role in the wizarding world.
Well, perhaps in the fanfiction, the Arcobaleno are intrigued by Harry's status as the Master of Death. They might seek his help to break a curse that is related to death in their world. Harry, in turn, could learn from the Arcobaleno's skills and powers, leading to an exchange of knowledge and a more complex, intertwined plot.
One idea could be exploring how Harry uses his newfound status as the Master of Death to bring back some of the characters who were lost in the war, like Sirius or Lupin. He could then form a new kind of magical order with them to safeguard the wizarding world in a different way.
Another plot could involve a prophecy that foretells the union of the Master of Death and a powerful magician like Zatanna to save all of magic from a looming catastrophe. Harry and Zatanna have to overcome cultural differences in their magical practices as well as external forces that are trying to prevent them from fulfilling the prophecy. They face challenges like misunderstandings among other wizards and witches who fear the power they might gain if they succeed.
Another plot could be that Harry is mistaken for someone else at Ouran. He then has to navigate through the misunderstandings while also trying to figure out how the Ouran world, with its own set of rules about class, social status, and relationships, compares to his world at Hogwarts. There could be a lot of comical moments as he tries to fit in without revealing his true identity as a wizard.
One plot idea could be that Harry, as the Master of Death, has the ability to see the true nature of Voldemort's Horcruxes more clearly. He uses this knowledge to track them down in a more efficient way. For example, he can sense the presence of a Horcrux in a place where Voldemort has hidden it well, like an ancient, cursed forest. Another idea is that Harry can communicate with the dead in a more profound way as the Master of Death. He could get advice from the founders of Hogwarts on how to defeat Voldemort once and for all.
Perhaps Harry, as the Young Master of Death, has to deal with the jealousy and fear of other wizards. Some might try to steal his power or use it for their own evil purposes. He could form an alliance with some unexpected characters, like the ghosts in Hogwarts, who help him understand and control his powers better.
Another plot could be that a powerful American dark wizard is using death as a weapon. He's creating an army of the undead or something similar. Harry, along with his friends Hermione and Ron (if they accompany him to America), has to find a way to stop this wizard. They might encounter unique American magical creatures that are either helping or hindering their mission. The story could explore the cultural differences between the American and British wizarding communities in the face of such a great threat.
One idea could be that the Goddess of Death has a special connection with Harry. For example, she might appear to him in a time of great danger and offer him a unique power that no one else has. This power could be related to seeing the true nature of dark magic, which would help him in his fight against Voldemort.
Perhaps in the fanfiction, the God of Death has a plan for Harry that involves not just his survival but also a complete transformation of the wizarding world. This could lead to Harry having to make some really tough choices between following the God of Death's plan and staying true to his friends and the values he has always held.