Perhaps Davy Jones' locker has a connection to the Chamber of Secrets. In the fanfiction, Harry discovers this link and has to journey into Davy Jones' locker to find a way to defeat Voldemort. Along the way, he has to face the horrors of the locker, including Davy Jones himself and his crew of the Flying Dutchman. This could be a really dark and exciting adventure.
Another concept could be that Davy Jones makes a deal with Orochimaru. In return for some powerful jutsu or access to certain secrets in the Naruto world, he offers Orochimaru a place in his crew. Naruto then has to stop this alliance from happening as it would bring great danger to his world. He could team up with some of the more morally upright pirates to take on Davy Jones and Orochimaru.
Well, it could be really strange and dark. Harry might grow up with a sense of the sea and the macabre. He could learn some of Davy Jones' cruel ways, but also perhaps inherit some of his power over the sea and the creatures in it.
In the Davy Jones story, Davy Jones was a sort of malevolent spirit of the ocean. He was associated with the deep sea and the fate of sailors. Sailors believed that if they died at sea, their souls would be claimed by Davy Jones. He was a powerful and somewhat mysterious figure in nautical mythology, with his 'locker' being a place where sunken ships and the souls of drowned sailors were thought to reside.
Another plot could involve the Hufflepuff's hard - working trait turning into something more sinister. The Hufflepuffs are working hard not for good grades or to help others, but to build a powerful dark force within the school. Harry, as a part of this dark Hufflepuff, slowly realizes what's going on and has to decide whether to join in or fight against it, all while being influenced by the dark undertones of the house.
One plot could be that in a dark version, Harry and Luna team up to expose a hidden, evil regime within the wizarding world that has been secretly controlling things from the shadows. They might have to use some rather unorthodox and darker magic to do so.
One plot could be that in a dark world, Harry Potter is influenced by dark magic and Tonks, with her Metamorphmagus abilities, tries to spy on him for the Order but gets caught in his web of newfound power. She has to then fight her own feelings as she was once his ally.
One possible plot could be that the female vampire is initially an enemy but then becomes an ally to Harry. Maybe she has some information about Voldemort's dark magic that is linked to her vampire lore. Another plot could be a love story where Harry has to overcome the fact that she's a vampire and deal with the wizarding world's reaction to their relationship.
One possible plot could be that female Harry Potter is wrongly accused and sent to Azkaban. There, she discovers a hidden conspiracy within the prison walls. Maybe she finds out that some dark wizards are using Azkaban as a base to plan an attack on Hogwarts. Another plot might involve her using her unique magic skills, different from the male Harry Potter's in some ways, to survive the Dementors and break free, all while uncovering the truth about her false imprisonment.
Harry's Patronus charm could be a very interesting element when it comes to interacting with Davy Jones. Since the Patronus is a positive and powerful form of magic, it could have an effect on the dark and cursed nature of Davy Jones and his crew. Maybe it could temporarily stun them or even start to break the curse on the crew. And Davy Jones' power over the kraken could be used against the wizarding world, but wizards could use their magic to either tame the kraken or create barriers to keep it at bay.
One possible plot could be that Hercules is transported to the wizarding world of Harry Potter. He might be mistaken for a powerful wizard at first due to his superhuman strength. Then, he could team up with Harry Potter and his friends to fight against a new dark threat that combines the magical and mythical evils. For example, a villain who can control both dark magic and mythical monsters.