There's also the possibility that it was a result of some time - travel or alternate reality situation where Harry had a relationship with someone like Sirius Black. This unorthodox relationship resulting in pregnancy would surely cause a stir in the wizarding world, forcing Harry to leave England to find a more accepting place.
Perhaps it's a completely new character, a powerful and mysterious wizard who came into Harry's life. Their encounter led to Harry's pregnancy, and the fear of this unknown wizard's intentions and the reaction of the English wizarding community makes Harry leave England.
One possible plot could be that Harry Potter discovers he is pregnant (through some magical means perhaps) and decides to leave England because he wants to protect his unborn child from the dark forces that still lurk in the country. He might go to a far - off magical land where he can raise the child in peace and secrecy.
He could meet new witches and wizards from different cultures. For example, he might run into a powerful African wizard who has unique magical abilities related to nature magic. Or he could meet a Japanese witch who specializes in charm - making that is based on ancient Shinto beliefs.
Maybe Harry leaves England to explore the wizarding world in other countries. He could go to France to study different magic spells at Beauxbatons Academy. Or perhaps he travels to America to help the MACUSA (Magical Congress of the United States of America) deal with some dark magic threats.
Well, Harry Potter is obviously one of the main characters. The other main character is often an original female character who is pregnant. She could be a witch that Harry has fallen in love with or a Muggle who got caught up in the wizarding world through Harry.
One possible story could be that Harry leaves England due to some family feud and the pregnant woman he's involved with decides to follow him. Maybe she's a Muggle who discovers the wizarding world through him and they embark on a journey to a new place where they can raise their child in peace.
One possible reason could be to protect Teddy. Maybe there are some threats in England that Harry wants to keep Teddy away from. For example, there could be some dark wizards or dangerous magical creatures that target Teddy for some reason.
They could go to France. France has a rich magical history and a large wizarding community. It would be a place where they could blend in and also learn new magical techniques. The Beauxbatons Academy of Magic is there, which could offer a different educational environment if they had children.
Perhaps it could be a character we haven't seen much in the 'Harry Potter' universe yet. A mysterious wizard who has some connection to Queenie's past or a new character introduced specifically for the fanfic. This could open up new storylines about the wizard's origin, his intentions, and how he fits into Queenie's life now that she's pregnant.
Obviously, the Queen of England would be one of the main characters. Harry Potter himself would also be a key character as he is the central figure in the Harry Potter universe. Maybe Hermione could also be involved as she is very intelligent and could help the Queen understand the wizarding world better.
A great 'Harry Potter Leaves England' fanfic should have a strong reason for Harry to leave. For example, if he's leaving to escape the trauma of the war or the overbearing attention. It also needs to have an interesting destination. If he goes to a place like Egypt with its rich magical history, it can add a lot to the story. Good character development is crucial too. We should see Harry evolving as he experiences new things in a different place.