Well, a really cool plot could be that Harry travels to a dimension where the wizarding world is merged with the Muggle world in a very chaotic way. He has to figure out how to keep the balance. Also, he might end up in a dimension where the Marauders are still alive and he gets to interact with them, which would be a great story of friendship and adventure. And there could be a dimension where magic is based on emotions and Harry has to learn to control his feelings to use magic effectively.
Well, in 'Harry Potter Dimensions Fanfiction', there could be a concept of a dimension where the wizarding world is at war with a completely different kind of dark force. Maybe a force from another dimension that uses a type of magic unknown to the normal wizarding world. Also, there might be a dimension where the Sorting Hat makes decisions based on different criteria, leading to a very different distribution of students among the houses. And perhaps a dimension where the magical creatures have a much more prominent role in society, almost like equal citizens.
First, you need to have a clear idea about the dimension you want to create. Decide on its unique features, like different magic rules or different character personalities. Then, think about how your story will start. It could be with a character accidentally stumbling into this new dimension. For example, Harry could find a hidden portal in Hogwarts that leads to a dimension where time moves differently.
He could meet his future children, if he has any. They would likely be powerful wizards or witches with their own adventures. Also, he might run into the future versions of Hermione and Ron. They would probably be in important positions in the wizarding world, like Hermione might be a headmistress at Hogwarts or something.
One possibility is that Naruto and Naruko are on a mission to save the multiverse in this fanfiction. They travel through dimensions to collect some special artifacts or powers that are scattered across different realities. Along the way, they might face challenges from the rulers of those dimensions who don't want them to take those things. This could involve epic battles and the forging of new alliances as they strive to complete their mission.
It could be some powerful dimension - hopping villains who want to use the power of different dimensions for their own evil purposes. They might see Naruto and Naruko as threats to their plans.
Perhaps Naruto travels to a dimension where everyone has a unique animal spirit companion. He has to bond with one of these spirits to gain access to certain powers. This would be a whole new experience for him as he's used to his own ninja world and its rules.
Maybe Neville. He has grown a lot in his magical abilities and his courage. He could bring his knowledge of herbology, which might be useful in different parts of the world. Luna Lovegood could also be a great companion. Her unique perspective on magic would help Harry see things in a different light during his travels.
He often meets versions of himself from different dimensions. These other Narutos might have different personalities or abilities due to the differences in their respective dimensions.