One possibility is that they leave England in search of a magical place that can offer them a peaceful life. They could be tired of the constant battles and power struggles in England. They might go to a far - off land where magic is used in a different, more harmonious way. For example, they could head to some hidden island where ancient magic thrives and they can study and grow without the interference of the Ministry or dark wizards.
In this fanfiction, they might leave England because they have a mission. They could have discovered some new magical phenomenon that requires them to leave the country to fully understand it. They could be on a journey to gather knowledge and allies, and England just doesn't have what they need at the moment. So, they set off on an adventure to other parts of the world.
It could be that Harry and Susan are escaping some sort of danger in England. They leave secretly and head to France. There, they try to blend in with the local community. Harry might find work as a painter and Susan could start teaching English. Their journey would be about not only starting anew but also constantly looking over their shoulders in case the danger from England follows them.
It's clear that Harry and Daphne are the main characters. Harry brings his courage, skills, and a network of friends (even if they're leaving England). Daphne may bring a different perspective, perhaps she has a more academic or cultural knowledge that will help them in the new places they'll visit. Their relationship and how they interact during this departure from England will likely be a major focus of the fanfiction.
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.
One possible reason could be to escape the danger and chaos that might be brewing in England within the wizarding world. Maybe there are dark forces targeting them specifically, and leaving is their only option for safety.
Well, perhaps in this fanfiction, Daphne is initially hesitant to befriend Harry because of his reputation. But then Harry saves her from some sort of danger in the Forbidden Forest. After that, they start to open up to each other. They might secretly practice new spells together and their friendship grows as they explore the secrets of Hogwarts that are not known to many. Their best - friendship could also lead to them bridging the gap between different houses in Hogwarts.
In the fanfiction, it could be that Daphne has some unique magical ability that she uses to protect Harry in Azkaban. They might encounter other inmates who are actually innocent too and together they start a mini - revolution against the unjust system of Azkaban. Harry, with his experience of facing Voldemort, might lead the way in finding a way out of the prison.
They could be two ordinary friends who have just decided that they need a change in their lives. Maybe they've grown up together in a small English town and now want to see what the world outside England has to offer.
In the fanfic, Sirius and Harry leaving England could lead them to a hidden magical island. There, Harry could learn different kinds of magic that are not taught at Hogwarts. Sirius would be able to protect Harry better as they are far away from the threats in England. They might also start a new life where Harry can grow up without the constant fear of Voldemort's followers finding him.
One reason could be to find peace. After all the chaos and war in England, they might just want to get away from it all and start fresh somewhere else.
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.