What could be the plot of a fanfic where Harry Potter saves Ace from One Piece?

A powerful magical creature that has a grudge against both Harry Potter and Ace. It might see Ace as an intruder in its territory in the Harry Potter universe and Harry as someone who is interfering. So it tries to stop Harry from saving Ace and becomes the main antagonist.

Well, Harry Potter might be magically transported to the 'One Piece' world just in time to save Ace. He could use his Patronus charm to fend off the attackers at Marineford. Since his Patronus is a powerful form of positive magic, it could be strong enough to hold off the Marines for a while. He might also use his knowledge of potions to heal Ace if he's already injured. And perhaps he forms an alliance with Luffy and the Straw Hats to help them get out of the dangerous situation at Marineford.

Well, in such a fanfic, perhaps Harry uses his magic skills like the Patronus charm to ward off any danger threatening Ace. Maybe he apparates into the scene just in time to pull Ace out of harm's way.

Well, it could be that Hedwig is poisoned by some magical substance. Harry, with the help of Hermione's research skills, figures out what the poison is. He then goes on a quest to find the antidote. Along the way, he faces many challenges like dangerous magical beasts and tricky spells. But in the end, he gets the antidote and saves Hedwig just in time.

Well, perhaps Harry uses his magic skills like the Patronus charm to fend off some dark force that is attacking the Avengers. He could also use his knowledge of potions to heal any injured Avengers.

One challenge could be the unfamiliarity with the Fairy Tail world. Different rules of magic and different types of magical creatures might be new to Harry. Another is that the Fairy Tail characters themselves might be very powerful and have their own unique abilities that Harry has to figure out how to counter.

Well, perhaps in this fanfic, Harry notices Draco in a dangerous situation with Buckbeak. Maybe Draco was taunting Buckbeak and it got out of hand. Harry, being the brave one, steps in and uses his skills with magical creatures to calm Buckbeak down just in time to save Draco from getting seriously hurt.

Well, perhaps Daphne somehow discovers Harry's awful situation at the Dursleys. She might use magic to break into the house secretly. Then she could use a spell to make the Dursleys forget about Harry so that she can take him away without a fuss.

Maybe the story shows Harry coming across Luna being bullied in a secluded part of Hogwarts. He steps in bravely, using his reputation as the 'Boy Who Lived' to intimidate the bullies into leaving Luna alone. He might also comfort Luna afterwards and form a stronger bond with her.

In the fanfiction, Fem Naruto might have some sort of special connection or knowledge. Since Naruto has a strong sense of justice, Fem Naruto would be the same. She might have heard about Ace's situation through some channels and decided to take action. She could use her chakra - enhanced strength to break through any barriers the marines set up to keep Ace captive.