How would a Harry Potter and Whitebeard fanfiction start?

It would be really strange and interesting. Maybe Harry Potter somehow gets transported to the One Piece world and meets Whitebeard. He could learn about Whitebeard's crew and their adventures, and perhaps use his magic in that world in unexpected ways.

One idea could be a crossover where Harry Potter accidentally travels to the One Piece world and meets Whitebeard. He could learn about their different forms of magic and power, and together they face a new threat that combines the dark magic from his world and the powerful pirates in the One Piece world.

A possible start could be a prophecy in both the wizarding world and Asgard. The prophecy foretells of a great danger that can only be averted if a wizard from Hogwarts and a warrior from Asgard join forces. Harry Potter and Thor are then made aware of this prophecy and set out on a journey to find each other and figure out how to stop the impending doom.

There could be. Fanfiction writers love to mix and match different elements from various fandoms. For a 'Harry Potter Whitebeard fanfiction', it may involve Whitebeard being a secret protector of the wizarding world. Maybe he has some ancient magic that is related to the magic in the Harry Potter universe. Writers might explore how his presence could change the course of events in the wizarding world, such as during the fight against Voldemort.

The fanfiction could start with Poison Ivy being magically transported to the wizarding world. She finds herself in the Forbidden Forest and starts to spread her influence among the native plants there. Harry Potter, while on a patrol in the forest, notices the strange changes in the plants and is the first to encounter Poison Ivy, leading to a tense first meeting between the two.

It could start with Harry having a strange dream about a cold, snowy land filled with direwolves. He wakes up curious and through some magical accident, ends up in the world where Brandon Stark lives. This sudden appearance in a new world full of different rules and politics would be the starting point of their adventure together.

Well, first, you need a unique idea. Maybe think about an untold story from a minor character's perspective or a 'what if' scenario. That could be a great starting point!

It could start with Harry being found as a baby in Rome. Maybe a Roman wizard family takes him in. They notice his special powers right away and start to train him in their ways.

It could start with a magical accident. For instance, a spell gone wrong in the Harry Potter world creates a portal that sucks the main character into the Highschool DxD world. Right from the start, he's greeted by some of the female characters in a rather interesting way that sets the harem aspect in motion.

Try searching on specialized fanfiction forums. There are often communities dedicated to specific crossovers or combinations of fandoms. They might have their own repositories or links to 'Harry Potter Whitebeard fanfiction'. Additionally, some social media groups related to Harry Potter or One Piece (where Whitebeard is from) may also share or discuss such fanfictions.