One possible plot could be that Harry Hook, who is used to his life in the Isle of the Lost, gets magically transported to Neverland. There, he meets Peter Pan. At first, they are at odds, as Harry is used to a more villainous lifestyle and Peter is the protector of Neverland. But as they face some common threats, like a new dark force that is trying to take over both their worlds, they start to work together. Along the way, they learn from each other's strengths and weaknesses, and in the end, they become friends and manage to defeat the threat.
A plot could involve Peter Pan being curious about the outside world beyond Neverland and somehow ending up in the Descendants' universe where he meets Harry Hook. Harry is intrigued by Peter's carefree and fearless nature. They decide to go on an adventure together in a new, strange land. However, they soon find out that a powerful enemy from their pasts has also made its way into this new world. They have to combine their skills, Peter's flying and ability to lead the Lost Boys, and Harry's sword - fighting and knowledge of the Isle of the Lost, to overcome this enemy and find their way back to their respective homes.
Perhaps Peater Pan's Daughter is on a mission to retrieve a magical item that has been stolen by the pirates led by Harry Hook. She infiltrates their ship and tries to steal it back, but Harry Hook catches her. Instead of punishing her immediately, he becomes intrigued by her. As they interact more, they realize they have more in common than they thought, and a relationship begins to form between them. This could involve a lot of adventure, like exploring hidden caves in Neverland and having to work together to defeat magical guardians of the caves.
There are several places you can look for 'Peater Pan meets Harry Hook' fanfics. One option is Archive of Our Own (AO3). It has a vast collection of fan - created works, and you can use the search function to specifically find stories related to these two characters. Another place could be FanFiction.net, though the quality and quantity might vary. You can also check out some Tumblr blogs dedicated to Descendants or Peter Pan fandoms as some fans might share or recommend such fanfics there.
There could be many such fanfics out there. However, without more specific details about what you're looking for in this fanfic (like the genre, whether it's a romantic or adventure - based story, etc.), it's difficult to recommend a particular one. Some fanfics might focus on their relationship development, while others could be part of a bigger adventure in Neverland. You really need to dig into the relevant fanfic communities to find the best one for you.
Perhaps Harry is on a trip outside of the wizarding world when he comes across Venom. At first, they are at odds as Venom views Harry as a potential threat. But as they get to know each other, they find out that they both have a sense of justice. Venom is impressed by Harry's magical abilities and Harry is intrigued by Venom's strength. They then team up to take on a common enemy, like a powerful sorcerer who is using dark magic to create chaos in both the Muggle and wizarding worlds.
One possible plot could be that the Hogwarts students are on a field trip when they accidentally stumble into the world of the Enterprise. Harry and his friends could help the Enterprise crew deal with a magical threat that the crew's technology can't handle. For example, a dark wizard has created a spell that is causing chaos on the Enterprise and only magic can reverse it.
One possible plot could be that Gaster somehow gets transported to the wizarding world of Harry Potter. He might initially be confused but then start to study the magic there. Maybe he tries to combine his own knowledge with magic, leading to some unique spells or potions. Harry and his friends could be both intrigued and cautious of this strange new character.
One possible plot could be that Pan, being from a different time period than Bardock, accidentally travels back in time and meets him. Maybe she initially mistakes him for Goku due to their similar Saiyan features. Bardock could be initially suspicious of her but then realize she has a good heart.
Well, perhaps Jack Frost accidentally enters Neverland while chasing a particularly strong winter wind. Peter Pan mistakes him for a new kind of fairy at first. Then they start to compete in various things, like who can fly faster (Jack using his ice - made wings and Peter with his pixie dust). But as they get to know each other, they realize they have a common enemy in Captain Hook, who wants to use Jack's ice powers to freeze the mermaids' lagoon and catch them easily. So they have to work together to stop Hook.
Well, it could be that Harry and Logan meet in a magical forest. Harry, being from his wizarding world, is intrigued by Logan's mutant abilities. Maybe they start by being cautious of each other, but then they realize they can help each other in some way, like Logan protecting Harry from some dark wizards who are after him for his magic, and Harry using his magic to heal Logan's wounds that won't heal on their own.
One possible interesting plot could be that the magic from the Harry Potter world starts to seep into the Percy Jackson universe, causing chaos among the demigods. For example, Hogwarts could suddenly appear in the middle of Camp Half - Blood. The demigods, not used to this type of magic, would be both curious and threatened. Meanwhile, Harry and his friends could get accidentally transported to the Percy Jackson world and have to team up with the demigods to figure out how to send Hogwarts back and restore the balance between the two magical systems.