A cool plot might be that Harry Potter is born with the soul of an ancient Valyrian king reincarnated. As he grows up in the wizarding world, he starts having strange dreams about Valyria. When he finally discovers the truth, he embarks on a journey to Valyria. There he meets descendants of the Valyrian people who teach him their lost arts of magic. He then uses this knowledge to bring about a new era of peace and cooperation between the two worlds, all while facing opposition from some who fear the change his rule as the 'King of Valyria' might bring.
One possible plot could be Harry Potter discovers he has some ancient connection to Valyria. Maybe he finds a hidden portal in Hogwarts that leads to the remnants of Valyria. There he could learn ancient magic that gives him new powers and he has to use these powers to fight off dark forces that are threatening both the wizarding world of Harry Potter and the remaining magic in Valyria.
The Death Eaters could be one group of antagonists. They might see Harry's newfound power and position as the King of Valyria as a threat to their plans for wizarding world domination. So they try to stop him from fully realizing his potential in Valyria and bringing back any new magic or alliances that could defeat them.
There might be a fanfiction where the dragons in Valyria are related to the dragons in the Harry Potter universe. For example, perhaps a spell from Harry Potter is used to control a Valyrian dragon, leading to all sorts of adventures and challenges for the characters.
In this fanfiction, it could be that the king is from an ancient line of wizards that have long been in hiding. When he adopts Harry, he reveals to Harry the true history of magic, which has been distorted over time. Harry then uses this knowledge to find new and powerful magical artifacts that help him defeat Voldemort once and for all. The king also provides Harry with a new family and a sense of belonging that he never really had at the Dursleys'.
In a 'Harry Potter King of Lions' fanfiction, a great plot could be that the lions are guardians of a powerful magic that can only be accessed by someone with a pure heart like Harry. The King of Lions tasks Harry with a series of trials. These trials are not only physical but also test his moral compass. For example, he has to choose between saving a group of innocent magical creatures or obtaining a magic item that could give him an edge in the fight against Voldemort. Through this journey, Harry grows in his understanding of magic and his own self - worth.
One possible plot could be that the Yautja King somehow gets transported to the Harry Potter universe. Maybe he's initially seen as a threat but then forms an alliance with Harry and his friends against a common dark enemy, like Voldemort. The Yautja King could bring his unique combat skills and advanced technology to the fight.
One possible interesting plot could be Harry forming an unexpected alliance with the spiders. Maybe he discovers a way to communicate with them on a deeper level and uses their knowledge of the Forbidden Forest to his advantage in a battle against the dark forces. For example, the spiders could lead him to a hidden magical artifact that has the power to defeat Voldemort.
Well, perhaps Harry discovers he has some hidden power that is related to King Ghidorah. Maybe he can transform into King Ghidorah - like form in times of great danger at Hogwarts, using his new - found abilities to protect the school from dark wizards. The other characters would be both amazed and a bit scared of this new Harry.
One possible plot could be that Harry discovers he has a hidden connection to the vampire world and is actually the heir to the 'King of Vampires'. He then has to balance his life at Hogwarts with his newfound vampiric identity, facing challenges from both the wizarding world that may fear him and the vampire world that may have its own power struggles.
Well, it might be about Harry Potter using his magic in a street - level setting, like maybe he's using magic to solve the problems of the common people on the streets. He could be like a secret hero among the street folk.
Well, it could be about Harry Potter somehow becoming the king in the North. Maybe he uses his magic in a new way to gain this position, ruling over a magical kingdom there.