Well, it could be about Angeal finding himself in the wizarding world of Harry Potter. Maybe he has to adapt to magic and the strange customs there while also using his own unique abilities from Final Fantasy. He could end up helping Harry Potter in his fight against Voldemort, perhaps with his sword skills and superhuman strength.
One possibility is that there's a threat that endangers both the world of Final Fantasy and the Harry Potter universe. Angeal and Harry Potter are brought together by a prophecy. They then embark on a journey to find the source of the threat. Along the way, they meet other characters from both universes. They face many challenges, such as dealing with dark wizards and powerful monsters from Final Fantasy. Angeal's stoic and noble nature would be a great complement to Harry's determination and courage.
One possible plot could be that Angeal is somehow transported to the Harry Potter universe. He might use his unique skills to help Harry in his fight against Voldemort. Maybe Angeal's combat abilities and sense of justice could be a great asset to the Order of the Phoenix.
Angeal has his powerful sword skills and superhuman strength. Harry has magic like the Patronus Charm. Maybe Angeal could use his physical strength to protect Harry while Harry uses magic to enhance Angeal's attacks. For example, Harry could cast a spell on Angeal's sword to make it cut through dark magic more easily.
In a 'Harry Potter Final Destination' fanfic, the plot could involve the Triwizard Tournament. The champions could start experiencing strange omens. Cedric Diggory, instead of being killed directly by Voldemort, could be the first to have a 'Final Destination' - like premonition of his death during a task. As he tries to avoid it, it sets off a chain of events that affects the other champions and the entire Hogwarts community. They all then have to figure out how to break this cycle of death.
There are some out there. You can start by looking on fanfic websites like Fanfiction.net or Archive of Our Own. Just search for 'Harry Potter x Angeal' and you'll likely find a variety of stories with different takes on this crossover concept.
The fanfic could center around Harry's life outside of the main events of the books. For example, it could explore his summer holidays in more detail. He could be spending time in the Muggle world and using his magic in creative ways to solve normal, everyday problems. He might use magic to help his neighbor fix a broken fence without the neighbor realizing it was magic. This would add a new dimension to his character and show how he can adapt his magical abilities to different situations.
One possible plot could be that Harry was wrongly imprisoned. Once released, he'd be on a quest to find out who framed him. He might start by gathering his old friends like Hermione and Ron. They would then dig into the dark secrets of the wizarding world that led to his false incarceration.
One idea could be to have Harry Potter characters enter the world of Final Fantasy VII. For example, Harry could end up in Midgar and meet Cloud. They could team up to fight against the dark forces in both their worlds, like Voldemort's minions and Sephiroth. The magic from the Harry Potter universe could interact in interesting ways with the materia and summons of Final Fantasy VII.
One possible plot could be that Harry Potter is hired by Sherlock Holmes to help with a case that involves dark magic. Harry uses his knowledge of the wizarding world to uncover clues that Sherlock couldn't find with just his deductive skills.
Imagine Harry Potter as a bartender. He could be using his skills not just in mixing drinks but also in reading people. Since he has faced so many challenges in his life, he can easily spot if a customer is hiding something or if they are in trouble. His bar could become a place where secrets are shared, and he has to use his wits and magic to keep things in order. He might also have to deal with rival bartenders from other wizarding establishments who are jealous of his popularity and unique drinks.
The plot could involve Harry Potter discovering he has some sort of connection to a dragoness. Maybe he can communicate with her telepathically. They could team up to fight against dark forces in the wizarding world. For example, Voldemort might be after the dragoness for her powerful magic, and Harry has to protect her while also using her strength to defeat Voldemort.